The conductance quantization and shot noise below the first conductance plateau $G_0 = 2e^2/h$ are measured in a quantum point contact fabricated in a GaAs/AlGaAs tunnel-coupled double quantum well. From the conductance measurement, we observe a clear quantized conductance plateau at $0.5G_0$ and a small minimum in the transconductance at $0.7 G_0$. Spectroscopic transconductance measurement reveals three maxima inside the first diamond, thus suggesting three minima in the dispersion relation for electric subbands. Shot noise measurement shows that the Fano factor behavior is consistent with this observation. We propose a model that relates these features to a wavenumber directional split subband due to a strong Rashba spin--orbit interaction that is induced by the center barrier potential gradient of the double-layer sample.
It is known that the conductance of a quantum point contact is quantized in units of $2e^2/h$ and this quantization is destroyed by a non-adiabatic scatterer in the point contact, due to backscattering. Recently, it was shown [Phys. Rev. Lett. 71, 137 (1993)] that taking many non-adiabatic scatterers periodically in a quantum channel, the quantization can be recovered. We study this conductance quantization of a periodic system in the presence of a strong defect. A periodic arrangement of double-stubs give remarkable quantization of conductance. A periodic arrangement of double-constrictions a…
We present numerical studies of conduction in graphene nanoribbons with different types of disorder. We find that even when defect scattering depresses the conductance to values two orders of magnitude lower than 2e^2/h, equally spaced conductance plateaus occur at moderately low temperatures due to enhanced electron backscattering near subband edge energies if bulk vacancies are present in the ribbon. This work accounts quantitatively for the surprising conductance quantization observed by Lin et al. [Phys. Rev. B 78, 161409 (2008)] in ribbons with such low conductances.
Notwithstanding the discreteness of metallic constrictions, it is shown that the finite elasticity of stable, single-atom gold constrictions allows for a continuous and reversible change in conductance, thereby enabling observation of channel saturation and conductance quantization. The observed channel saturation and signature for conductance quantization is achieved by superposition of atomic/subatomic-scale oscillations on a retracting/approaching gold tip against a gold substrate of a scanning probe. Results also show that conductance histograms are neither suitable for evaluating the stab…
Recent experiments on atomic-scale metallic contacts have shown that the quantization of the conductance appears clearly only after the average of the experimental results. Motivated by these results we have analyzed a simplified model system in which a narrow neck is randomly coupled to wide ideal leads, both in absence and presence of time reversal invariance. Based on Random Matrix Theory we study analytically the probability distribution for the conductance of such system. As the width of the leads increases the distribution for the conductance becomes sharply peaked close to an integer mu…
We fabricated strongly confined Schottky-gated quantum point contacts by etching Si/SiGe heterostructures and observed intriguing conductance quantization in units of approximately 1e2/h. Non-linear conductance measurements were performed depleting the quantum point contacts at fixed mode-energy separation. We report evidences of the formation of a half 1e2/h plateau, supporting the speculation that adiabatic transmission occurs through 1D modes with complete removal of valley and spin degeneracies.
We have studied ballistic transport in a 1D channel formed using surface gate techniques on a back-gated, high-mobility, bilayer 2D hole system. At millikelvin temperatures, robust conductance quantization is observed in the quantum wire formed in the top layer of the bilayer system, without the gate instabilities that have hampered previous studies of 1D hole systems. Using source drain bias spectroscopy, we have measured the 1D subband spacings, which are 5-10 times smaller than in comparable GaAs electron systems, but 2-3 times larger than in previous studies of 1D holes. We also report the…
We consider electron waveguides (quantum wires) in graphene created by suitable inhomogeneous magnetic fields. The properties of uni-directional snake states are discussed. For a certain magnetic field profile, two spatially separated counter-propagating snake states are formed, leading to conductance quantization insensitive to backscattering by impurities or irregularities of the magnetic field.
We report on the fabrication and electronic transport characterisation of Schottky-gated strongly confined Si/SiGe quantum point contacts (QPC). At zero magnetic field and T=450mK the QPC conductance as a function of gate voltage shows a quantization in units of e^2/h, indicative of transport through 1D modes which appear to lack both spin and valley degeneracy.
The controlled fabrication of well-ordered atomic-scale metallic contacts is of great interest: it is expected that the experimentally observed high percentage of point contacts with a conductance at non-integer multiples of the conductance quantum G_0 = 2e^2/h in simple metals is correlated to defects resulting from the fabrication process. Here we demonstrate a combined electrochemical deposition and annealing method which allows the controlled fabrication of point contacts with pre-selectable integer quantum conductance. The resulting conductance measurements on silver point contacts are co…
We study numerically the effects of edge and bulk disorder on the conductance of graphene nanoribbons. We compute the conductance suppression due to localization induced by edge scattering. We find that even for weak edge roughness, conductance steps are suppressed and transport gaps appear. These gaps are approximately inversely proportional to the nanoribbon width. On/off conductance ratios grow exponentially with the nanoribbon length. Our results impose severe limitations to the use of graphene in ballistic nanowires.
The electric conductance of Rh atomic contacts was investigated under the electrochemical potential control. The conductance histogram of Rh atomic contacts varied with the electrochemical potential. When the electrochemical potential of the contact was kept at $Φ_{0}$= 0.1 V vs. Ag/AgCl (Rh potential), the conductance histogram did not show any features. At $Φ_{0}$= -0.1 V (under potential deposited hydrogen potential), the conductance histogram showed a feature around 2.3 $G_{0}$ ($G_{0}$ =2$e^{2}/h$), which agreed with the conductance value of a clean Rh atomic contact, which was observed i…
The conductance of a single-atom contact is sensitive to the coupling of this contact atom to the atoms in the leads. Notably for the transition metals this gives rise to a considerable spread in the observed conductance values. The mean conductance value and spread can be obtained from the first peak in conductance histograms recorded from a large set of contact-breaking cycles. In contrast to the monovalent metals, this mean value for Pt depends strongly on the applied voltage bias and other experimental conditions, ranging from about 1 to 2.5 times 2e^2/h. We propose that the different resu…
We theoretically study the electron transport through a magnetic point contact (PC) with special attention to the effect of an atomic scale domain wall (DW). The spin precession of a conduction electron is forbidden in such an atomic scale DW and the sequence of quantized conductances depends on the relative orientation of magnetizations between left and right electrodes. The magnetoresistance is strongly enhanced for the narrow PC and oscillates with the conductance.
Using a generalized Landauer approach we study the non-linear transport in mesoscopic graphene with zig-zag and armchair edges. We find that for clean systems, the low-bias low-temperature conductance, G, of an armchair edge system in quantized as G/t=4 n e^2/h, whereas for a zig-zag edge the quantization changes to G/t t=4(n+1/2)e^2/h, where t is the transmission probability and n is an integer. We also study the effects of a non-zero bias, temperature, and magnetic field on the conductance. The magnetic field dependence of the quantization plateaus in these systems is somewhat different from…
We present an original method to estimate the conductivity of a single molecule anchored to nanometric-sized metallic electrodes, using a Mechanically Controlled Break Junction (MCBJ) operated at room temperature in liquid. We record the conductance through the metal / molecules / metal nanocontact while keeping the metallic electrodes at a fixed distance. Taking advantage of thermal diffusion and electromigration, we let the contact naturally explore the more stable configurations around a chosen conductance value. The conductance of a single molecule is estimated from a statistical analysis …
Recently it has been observed that the conductance fluctuations of atomic size gold contacts are suppressed when the conductance is equal to an integer multiple of the conductance quantum. The fact that these contacts tend to consist exclusively of fully open or closed modes has been argued to be the origin for this suppression. Here, the experiments have been extended to a wide range of metallic elements with different chemical valence and they provide new information about the relation between the mode composition and statistically preferred conductance values observed in conductance histogr…
Using scanning tunneling microscopy (STM), we investigated the evolution of electrical conductance between a Pb tip and Pb(111) surface from tunneling to atomic point contact at a site that was defined with atomic precision. We found that the conductance evolution depended on the contact site, for instance, on-top, bridge, or hollow (hcp and fcc) sites in the Pb lattice. In the transition from tunneling to contact regimes, the conductance measured at the on-top site was enhanced. In the point contact regime, the hollow sites had conductances larger than those of the other sites, and between th…
We analyze the fractional quantization of the ballistic conductance associated with the light and heavy holes bands in Si, Ge and GaAs systems. It is shown that the formation of the localized hole state in the region of the quantum point contact connecting two quasi-1D hole leads modifies drastically the conductance pattern. Exchange interaction between localized and propagating holes results in the fractional quantization of the ballistic conductance different from those in electronic systems. The value of the conductance at the additional plateaux depends on the offset between the bands of t…
We present the results of million atom electronic quantum transport calculations for graphene nanoconstrictions with edges that are smooth apart from atomic scale steps. We find conductances quantized in integer multiples of 2e2/h and a plateau at ~0.5*2e2/h as in recent experiments [Tombros et al., Nature Physics 7, 697 (2011)]. We demonstrate that, surprisingly, conductances quantized in integer multiples of 2e2/h occur even for strongly non-adiabatic electron backscattering at the stepped edges that lowers the conductance by one or more conductance quanta below the adiabatic value. We also …
Theory and a vast set of experimental work in metals, since a century, appear to show that the mean free path of conduction electrons in a real metal is about the min (bulk mean free path, smallest transversal size of the metal), a result that was already proposed by J. J. Thomson in 1901. This establishes, as discussed in this work, serious difficulties to justify conductance quantization and ballistic transport in atomic/nanocontacts or nanoconstrictions of real life metals. The ohmic resistance of the leads proves to be as important as the ballistic one of the constriction.
Motivated by recent experiments [Science 355, 6330 (2017); Nat. Nanotechnol. 12, 430 (2017)], we present here an extensive theoretical analysis of the thermal conductance of atomic-size contacts made of three different metals, namely gold (Au), platinum (Pt) and aluminum (Al).
Ballistic transport through an impurity-free section of the Corbino disk in graphene is investigated by means of the Landauer-Büttiker formalism in the mesoscopic limit. In the linear-responce regime the conductance is quantized in steps close to integer multiples of $4e^{2}/h$, yet Fabry-Perot oscillations are strongly suppressed. The quantization arises for small opening angles $θ\lesssimπ/3$ and large radii ratios $R_2/R_1\gtrsim{}10$. We find that the condition for emergence of the $n$-th conductance step can be written as $\sqrt{n}θ/π\ll{}1$. A brief comparison with the conductance spectr…
We study the thermal conductance of ballistic point contacts. These contacts are realized as few nanometer long pillars in so called air-gap heterostructures (AGHs). The pillar length being much smaller that the mean free path of the phonons up to room temperature. Due to the small dimension and the low density of the pillars the thermal conductance of the AGHs is several orders of magnitude reduced in comparison to bulk structures. The measurement results are in quantitative agreement with a simple model that based on the Boltzmann transport equation.
Microwave induced photoconductivity of a two-dimensional electron gas (2DEG) in selectively-doped GaAs/AlAs heterostructures has been studied using the Corbino geometry with capacitive contacts at a temperature T=1.6K and magnetic field B up to 0.5 T. Zero-conductance states have been observed in the samples under study subject to microwave radiation, similarly to the samples with ohmic contacts. It has been shown that ohmic contacts do not play a significant role for observation of zero-conductance states induced by microwave radiation
Self-consistent modelling based on local spin-density formalism is employed to calculate conductance of quantum point contacts at finite temperatures. The total electrostatic potential exhibits spin-dependent splitting, which persists at temperatures up to 0.5 K and gives rise to the anomalies at 0.4 and 0.7 of the conductance quantum $2e^2/h$ occurring simultaneously in the absence of external magnetic fields.
The influence of a quantizing magnetic field $H$ to the conductance of a tunnel point contact in the presence of the single defect has been considered. We demonstrate that the conductance exhibits specific magneto-quantum oscillations, the amplitude and period of which depend on the distance between the contact and the defect. We show that a non-monotonic dependence of the point-contact conductance results from a superposition of two types of oscillations: A short period oscillation arising from electron focusing by the field $H$ and a long period oscillation of Aharonov-Bohm-type originated f…
We calculate the non-linear conductance of a quantum point contact using the non-equilibrium Greens function technique within the Hartree approximation of spinless electrons. We quantitative reproduce the 0.25-anomaly in the differential conductance (i.e. the lowest plateau at 0.25-0.3*2e^2/h) as well as an upward bending of higher conductance half-integer plateaus seen in the experiments, and relate these features to the non-linear screening and pinning effects.
By using bosonization method and unitary transformation, we give a general relation between the dimensionless tunneling conductance and the fractional Coulomb blockade conductance peak splitting which is valid both for weak and strong transmission between two quantum dots, and show that the tunneling conductance has a linear temperature dependence in the low energy and low temperature limit.
When monatomic contacts are stretched, their conductance behaves in qualitatively different ways depending on their constituent atomic elements. Under a single assumption of resonance formation, we show that various conductance behavior can be understood in a unified way in terms of the response of the resonance to stretching. This analysis clarifies the crucial roles played by the number of valence electrons, charge neutrality, and orbital shapes.
The conductance of atomic size contacts has a small, random, voltage dependent component analogous to conductance fluctuations observed in diffusive wires (UCF). A new effect is observed in gold contacts, consisting of a marked suppression of these fluctuations when the conductance of the contact is close to integer multiples of the conductance quantum. Using a model based on the Landauer-Buettiker formalism we interpret this effect as evidence that the conductance tends to be built up from fully transmitted (i.e., saturated) channels plus a single, which is partially transmitted.
Ballistic electron transport is a key requirement for existence of a topological phase transition in proximitized InSb nanowires. However, measurements of quantized conductance as direct evidence of ballistic transport have so far been obscured due to the increased chance of backscattering in one dimensional nanowires. We show that by improving the nanowire-metal interface as well as the dielectric environment we can consistently achieve conductance quantization at zero magnetic field. Additionally, studying the sub-band evolution in a rotating magnetic field reveals an orbital degeneracy betw…
In paper [1] (Avotina et al. Phys. Rev. B,74, 085411 (2006)) the effect of Fermi surface anisotropy to the conductance of a tunnel point contact, in the vicinity of which a single point-like defect is situated, has been investigated theoretically. The oscillatory dependence of the conductance on the distance between the contact and the defect has been found for a general Fermi surface geometry. In this paper we apply the method developed in [1] to the calculation of the conductance of noble metal contacts. An original algorithm, which enables the computation of the conductance for any parametr…
Hall conductance $σ_{xy}$ as the Chern numbers of the Berry connection in the magnetic Brillouin zone is calculated for a realistic multi band tight-band model of graphene with non-orthogonal basis. It is confirmed that the envelope of $σ_{xy}$ coincides with a semi-classical result when magnetic field is sufficiently small. The Hall resistivity $ρ_{xy}$ from the weak-field Boltzmann theory also explains the overall behaviour of the $σ_{xy}$ if the Fermi surface is composed of a single energy band. The plateaux of $σ_{xy}$ are explained from semi-classical quantization and necessary modificati…
Most quantum point contacts (QPCs) fabricated in high-mobility 2D electron gases show a zero-bias conductance peak near pinchoff, but the origin of this peak remains a mystery. Previous experiments have primarily focused on the zero-bias peak at moderate conductance, in the range (1-2)e^2/h. Here, measurements are presented of zero-bias peaks that persist down to 10^{-4}e^2/h. Magnetic field and temperature dependencies of the zero-bias peak in the low-conductance limit are qualitatively different from the analogous phenomenology at higher conductance, with implications for existing theoretica…
We formulate and prove an exact relation which expresses the moments of the two-point conductance for an open disordered electron system in terms of certain density correlators of the corresponding closed system. As an application of the relation, we demonstrate that the typical two-point conductance for the Chalker-Coddington model at criticality transforms like a two-point function in conformal field theory.
We report on a striking departure from the canonical step sequence of quantized conductance in a ballistic, quasi-one-dimensional metallic channel. Ideally, in such a structure, each sub-band population contributes its Landauer conductance quantum independently of the rest. In a picture based exclusively on coherent single-carrier transmission, unitary back-scattering can lower a conductance step below ideal, but it is absolutely impossible for it to enhance the ideal Landauer conductance of a sub-band. Precisely such an anomalous and robust nonlinear enhancement has already been observed over…
Conductance quantization was measured in submicron constrictions of PbTe, patterned into narrow,12 nm wide quantum wells deposited between Pb$_{0.92}$Eu$_{0.08}$Te barriers. Because the quantum confinement imposed by the barriers is much stronger than the lateral one, the one-dimensional electron energy level structure is very similar to that usually met in constrictions of AlGaAs/GaAs heterostructures. However, in contrast to any other system studied so far, we observe precise conductance quantization in $2e^2/h$ units, {\it despite of significant amount of charged defects in the vicinity of …
The electronic and transport properties of atomic-size contacts are analyzed theoretically using a self-consistent tight-binding model. Our results show that, for s-like metals, a sufficiently narrow contact exhibits well defined resonant states at the Fermi energy, spatially localized in the neck region. These states are robust with respect to disorder and provide a simple explanation for the observed tendency to conductance quantization. It is also shown that these properties disappear for a sufficiently large contact area. The possible relevance of this resonant states in scanning tunneling…
Electron flow through a quantum point contact in presence of spin-orbit coupling is investigated theoretically in the context of the scanning gate microscopy (SGM) conductance mapping. Although in the absence of the floating gate the spin-orbit coupling does not significantly alter the conductance, we find that the angular dependence of the SGM images of the electron flow at the conductance plateaux is substantially altered as the spin-orbit interaction mixes the orbital modes that enter the quantum point contact. The radial interference fringes that are obtained in the SGM maps at conductance…
The quantum of heat conductance of ballistic one-dimensional (1D) channels, being gQ=k0T with k0=pi^2*2kB^2/3h (T - temperature, kB - Boltzmann's constant, h - Planck's constant), is an important fundamental constant. While the quantization of the electrical conductance of 1D ballistic conductors has long been experimentally established, a demonstration of the quantization of thermal conductance proved to be much harder. It has already been accomplished for weakly interacting systems of phonons, photons, and electronic Fermi-liquids. Theoretically, however, the quantization must also hold in s…
A recursive Green's function technique is developed to calculate the spin-dependent conductance in mesoscopic structures. Using this technique, we study the spin-dependent electronic transport of quantum point contacts in the presence of the Rashba spin-orbit interaction. We observed that some oscillations in the `quantized' conductance are induced by the spin-orbit interaction, and indicated that the oscillations may stem from the spin-orbit coupling associated multiple reflections. It is also indicated that the 0.7 structure of the conductance observed in mesoscopic experiments would not ste…
We present detailed experimental studies of the temperature dependence of the plateau conductance of GaAs quantum point contacts in the temperature range from 0.3 K to 10 K. Due to a strong lateral confinement produced by a shallow-etching technique we are able to observe the following unexpected feature: a linear temperature dependence of the measured mid-plateau conductance. We discuss an interpretation in terms of a temperature dependent, intrinsic series resistance, due to non-ballistic effects in the 2D-1D transition region. These results have been reproduced in several samples from diffe…
Many experiments have shown that the conductance histograms of metallic atomic-sized contacts exhibit a peak structure, which is characteristic of the corresponding material. The origin of these peaks still remains as an open problem. In order to shed some light on this issue, we present a theoretical analysis of the conductance histograms of Au atomic contacts. We have combined classical molecular dynamics simulations of the breaking of nanocontacts with conductance calculations based on a tight-binding model. This combination gives us access to crucial information such as contact geometries,…
Despite topological protection and the absence of magnetic impurities, two-dimensional topological insulators display quantized conductance only in surprisingly short channels, which can be as short as 100 nm for atomically thin materials. We show that the combined action of short-range nonmagnetic impurities located near the edges and on site electron-electron interactions effectively creates noncollinear magnetic scatterers, and, hence, results in strong backscattering. The mechanism causes deviations from quantization even at zero temperature and for a modest strength of electron-electron i…
Atomic-sized junctions of iron, created by controlled rupture, present unusually high values of conductance compared to other metals. This result is counter-intuitive since, at the nanoscale, body-centered cubic metals are expected to exhibit lower coordination than face-centered cubic metals. In this work, classical molecular dynamics simulations of contact rupture, using an interatomic potential that accounts for directional bonding, yield highly-coordinated stable structures before rupture, unlike an isotropic bonding potential, which results in the expected stable single-atom contacts. Den…
We present numerical studies of non-linear conduction in graphene nanoribbons when a bias potential is applied between the source and drain electrodes. We find that the conductance quantization plateaus show asymmetry between the electron and hole branches if the potential in the ribbon equals the source or drain electrode potential and strong electron (hole) scattering occurs. The scattering may be at the ends of a uniform ballistic ribbon connecting wider regions of graphene or may be due to defects in the ribbon. We argue that, in ribbons with strong defect scattering, the ribbon potential …
In the present article we give a brief overview of the theories of the 0.7 anomaly of the ballistic conductance. The special attantion is given to the concept of a fractional quantization of the ballistic conductance arising from exchange interaction of the Heisenberg type between the carrier localized in the region of the quantum point contact and freely propagating carriers in electron and hole systems. ----- Brotaskömmtun skotleiðninnar í einvíðum rafeinda og holukerfum Í grein þessari verður skömmtun skotleiðninnar í einvíðum kerfum útskýrð og farið yfir nýjustu og helstu fræðilíkön á svið…
The interplay between groups of water molecules and single-atom contacts, as reflected in the electrical conductances and mechanical forces of copper atomic junctions, is explored by means of first-principles theory and semi-empirical calculations. We study the influence of the atomic geometries of copper electrodes with pyramidal and non-crystalline structures in the presence and absence of water on the conductance profiles as the electrodes approach each other. It is shown that the atomic arrangements of nano-contacts have crucial effects on the formation of plateaus and the conductance valu…
Using the recursive Green's function technique, we study the coherent electron conductance of a quantum point contact in the presence of a scanning probe microscope tip. Images of the coherent fringe inside a quantum point contact for different widths are obtained. It is found that the conductance of a specific channel is reduced while other channels are not affected as long as the tip is located at the positions correspending to that channel. Moreover, the coherent fringe is smoothed out by increasing the temperature or the voltage across the device. Our results are consistent with the experi…
We present a theoretical analysis of recent experimental results of Yacoby et al. on transport properties of high quality quantum wires. We suggest an explanation of observed deviations of the conductance from the universal value $2e^2/h$ per channel in the wire. We argue that at low temperatures and biases the deviation can be a consequence of anomalously enhanced backscattering of electrons entering the 2DEG from the wire and is not connected to intrinsic properties of 1DEG.
The electrical transport properties of atomic-scale conductors are reviewed, with an emphasis on the relations of this problem with studies on quantum size effects in metallic clusters. A brief introduction is given of the natural formalism for discussing electron transport in ballistic conductors: the Landauer theory. After introducing the experimental techniques, which are used for studying ballistic point contacts in metals, the experimental observations for the conductance of atomic-scale contacts are presented. In order to obtain a full description in terms of the quantum modes for conduc…
Recently, different experiments on the transport through atomic-sized contacts made of ferromagnetic materials have produced contradictory results. In particular, several groups have reported the observation of half-integer conductance quantization, which requires having full spin polarization and perfectly conducting channels. Motivated by these surprising results, we have studied theoretically the conductance of ideal atomic contact geometries of the ferromagnetic 3d materials Fe, Co, and Ni using a realistic tight-binding model. Our analysis shows that in the absence of magnetic domains, th…
The electron transport in a four-terminal nanodevice consisting of two crossed nanotubes is investigated in the framework of the Landauer-Buttiker formalism. The evident formula for the ballistic conductance of the device is found using a model of crossed conductive cylinders with a point contact between them. Sharp conductance dips stipulated by resonance scattering on the contact are shown to appear in the conductance of the first cylinder. The conductance between the cylinders has resonant behavior. The form and the position of resonant peaks are studied. Our results indicate that the form …
Recent experiments on the conductance of high quality quantum wires have revealed an unexpected feature: the quantization step of the conductance is apparently system dependent. We provide the understanding of this behaviour using the appropriately extended random matrix approach. A single additional parameter governs the size of the conductance quantization steps. In effect the behaviour seems to remain `universal', generic for the conductance of a class of mesoscopic systems.
We study theoretically the conductance of heterostructures with ferromagnetic conductors (F) and a two dimensional electron gas with Rashba spin-orbit interaction (R) using the Landauer-Büttiker formalism. Assuming a one-dimensional model, we first find the $S$-matrix for the FR interface. This result is then applied to different devices such as a FRF structure, first suggested by Datta and Das[Appl. Phys. Lett. 56, 665 (1990)]. We find analytic results for the conductance for the case of collinear magnetization.
The temperature dependence of the conductance of a quantum point contact has been measured. The conductance as a function of the Fermi energy shows temperature-independent fixed points, located at roughly multiple integers of $e^{2}/h$. Around the first fixed point at e$^{2}$/h, the experimental data for different temperatures can been scaled onto a single curve. For pure thermal smearing of the conductance steps, a scaling parameter of one is expected. The measured scaling parameter, however, is significantly larger than 1. The deviations are interpreted as a signature of the potential landsc…
We report the experimental observation of conductance quantization in graphene nanoribbons, where 1D transport subbands are formed due to the lateral quantum confinement. We show that this quantization in graphene nanoribbons can be observed at temperatures as high as 80 K and channel lengths as long as 1.7 $μ$m. The observed quantization is in agreement with that predicted by theoretical calculations.
The effects of electron interaction on the magnetoconductance of graphene nanoribbons (GNRs) are studied within the Hartree approximation. We find that a perpendicular magnetic field leads to a suppression instead of an expected improvement of the quantization. This suppression is traced back to interaction-induced modifications of the band structure leading to the formation of compressible strips in the middle of GNRs. It is also shown that the hard wall confinement combined with electron interaction generates overlaps between forward and backward propagating states, which may significantly e…
