Strain enhanced electron cooling in a degenerately doped semiconductor
M. J. Prest, J. T. Muhonen, M. Prunnila, D. Gunnarsson, V. A. Shah, J. S. Richardson-Bullock, A. Dobbie, M. Myronov, R. J. H. Morris, T. E. Whall, E. H. C. Parker, D. R. Leadley
Enhanced electron cooling is demonstrated in a strained-silicon/superconductor tunnel junction refrigerator of volume 40 um^3. The electron temperature is reduced from 300 mK to 174 mK, with the enhancement over an unstrained silicon control (300 mK to 258 mK) being attributed to the smaller electron-phonon coupling in the strained case. Modeling and the resulting predictions of silicon-based cooler performance are presented. Further reductions in the minimum temperature are expected if the junction sub-gap leakage and tunnel resistance can be reduced. However, if only tunnel resistance is reduced, Joule heating is predicted to dominate.
Resonant microwave-assisted and DC transport are investigated in degenerately doped silicon single electron transistors. A model based on hopping via localized impurity states is developed and first used to explain both the DC temperature dependence and the AC response. In particular, the non-monotonic power dependence of the resonant current under irradiation is proved to be consistent with spatial Rabi oscillations between these localized states.
We report low-frequency 1/f noise measurements of degenerately doped Si:P δ-layers at 4.2K. The noise was found to be over six orders of magnitude lower than that of bulk Si:P systems in the metallic regime and is one of the lowest values reported for doped semiconductors. The noise was found to be nearly independent of magnetic field at low fields, indicating negligible contribution from universal conductance fluctuations. Instead interaction of electrons with very few active structural two-level systems may explain the observed noise magnitude
We report electrical spin injection and detection in degenerately doped n-type Ge channels using Mn5Ge3C0.8/Al2O3/n^{+}-Ge tunneling contacts for spin injection and detection. The whole structure is integrated on a Si wafer for complementary metal-oxide-semiconductor compatibility. From three-terminal Hanle-effect measurements, we observe a spin accumulation up to 10 K. The spin lifetime is extracted to be 38 ps at T = 4K using Lorentzian fitting, and the spin diffusion length is estimated to be 367 nm due to the high diffusion coefficient of the highly doped Ge channel.
In search of an improved strategy to form low resistance contacts to MoS2 and related semiconducting transition metal dichalcogenides, we use ab initio density functional electronic structure calculations in order to determine the equilibrium geometry and electronic structure of MoO3/MoS2 and MoO2/MoS2 bilayers. Our results indicate that, besides a rigid band shift associated with charge transfer, the presence of molybdenum oxide modifies the electronic structure of MoS2 very little. We find that the charge transfer in the bilayer provides a sufficient degree of hole doping to MoS2, resulting …
As a high-order quantum transition, two-photon emission has an extremely low occurrence rate compared to one-photon emission, thus having been considered a forbidden process. Here, we propose a scheme that allows ultrafast two-photon emission, leveraging highly confined surface plasmon polariton modes in a degenerately-doped, light-emitting semiconductor thin film. The surface plasmon polariton modes are tailored to have simultaneous spectral and spatial overlap with the two-photon emission in the semiconductor. Using degenerately-doped InSb as the prototype material, we show that the two-phot…
We report charge detection in degenerately phosphorus-doped silicon double quantum dots (DQD) electrically connected to an electron reservoir. The sensing device is a single electron transistor (SET) patterned in close proximity to the DQD. Measurements performed at 4.2K show step-like behaviour and shifts of the Coulomb Blockade oscillations in the detector's current as the reservoir's potential is swept. By means of a classical capacitance model, we demonstrate that the observed features can be used to detect single-electron tunnelling from, to and within the DQD, as well as to reveal the DQ…
The search for half-metals and spin-gapless semiconductors has attracted extensive attention in material design for spintronics. Existing progress in such a search often requires peculiar atomistic lattice configuration and also lacks active control of the resulting electronic properties. Here we reveal that a boron-nitride nanoribbon with a carbon-doped edge can be made a half-metal or a spin-gapless semiconductor in a programmable fashion. The mechanical strain serves as the on/off switches for functions of half-metal and spin-gapless semiconductor to occur. Our findings shed light on how th…
In Weyl semimetals, there is an intriguing possibility of realizing a pseudo-magnetic field in presence of small strain due to certain special cases of static deformations. This pseudo-magnetic field can be large enough to form quantized Landau levels and thus become observable in Weyl semimetals. In this paper, we experimentally show the emergence of a pseudo-magnetic field (~ 3 Tesla) by Scanning Tunneling Spectroscopy (STS) on the doped Weyl semimetal Re-MoTe2, where distinct Landau level oscillations in the tunneling conductance are clearly resolved. The crystal lattice is intrinsically st…
A theoretical model for the calculation of the phonon-drag thermopower, $S^{g}$, in degenerately doped semiconducting single-wall carbon nanotubes (SWCNTs) is proposed. Detailed calculations of $S^{g}$ are performed as a function of temperature, tube radius and position of the Fermi level. We derive a simple analytical expression for $S^{g}$ that can be utilized to determine the free carrier density in doped nanotubes. At low temperatures $S^{g}$ shows an activated behavior characteristic of the one-dimensional (1D) character of carriers. Screening effects are taken into account and it is foun…
Reliable detection of single electron tunneling in quantum dots (QD) is paramount to use this category of device for quantum information processing. Here, we report charge sensing in a degenerately phosphorus-doped silicon QD by means of a capacitively coupled single-electron tunneling device made of the same material. Besides accurate counting of tunneling events in the QD, we demonstrate that this architecture can be operated to reveal asymmetries in the transport characteristic of the QD. Indeed, the observation of gate voltage shifts in the detector's response as the QD bias is changed is …
We demonstrate theoretically that a new system quantum well can realize the topological transition based on the 16-band kp model. Utilizing the strain introduced by the doped impurities, the band anti crossing induced by the doped nitrogen and valence band anti crossing induced by the doped bismuth, the band gap of the quantum well is rapidly decreased and even becomes negative. As a result, the topological transitions arise. Furthermore, the band gap as a function of the concentration of nitrogen and bismuth is calculated, where the negative gap corresponds to the topological phase. Noting th…
The effects of biaxial strain on the impurity-induced magnetism in P-doped graphene (P-graphene) and N-doped silicene (N-silicene) are studied by means of spin-polarized density functional calculations, using the supercell approach. The calculations were performed for three different supercell sizes $4\times 4$, $5\times 5$, and $6\times 6$, in order to simulate three different dopant concentrations 3.1, 2.0 and 1.4 %, respectively. For both systems, the calculated magnetic moment is 1.0 $μ_B$ per impurity atom for the three studied concentrations. From the analysis of the electronic structure…
Graphene, due to its exceptional properties, is a promising material for nanotechnology applications. In this context, the ability to tune the properties of graphene-based materials and devices with the incorporation of defects and impurities can be of extraordinary importance. Here we investigate the effect of uniaxial tensile strain on the electronic and magnetic properties of graphene doped with substitutional Ni impurities (Ni_sub). We have found that, although Ni_sub defects are non-magnetic in the relaxed layer, uniaxial strain induces a spin moment in the system. The spin moment increas…
The effects of biaxial tensile strain on the structure, electronic states, and mechanical properties of silicene are studied by ab-initio calculations. Our results show that up to 5% strain the Dirac cone remains essentially at the Fermi level, while higher strain induces hole doping because of weakening of the Si$-$Si bonds. We demonstrate that the silicene lattice is stable up to 17% strain. It is noted that the buckling first decreases with the strain (up to 10%) and then increases again, which is accompanied by a band gap variation. We also calculate the Grüneisen parameter and demonstrate…
We show that a spontaneous strain and spontaneous magnetization can arise in the doped topological insulators with a two-component superconducting vector order parameter. The details of the effects crucially depend on the symmetry of the superconducting order parameter, whether it is nematic or chiral. The transition from the nematic state to the chiral one can be performed by application of a magnetic field while the transition from the chiral state to the nematic one is tuned by the external strain. These transitions associated with a jump of the magnetic susceptibility and mechanical stiffn…
The electron transport in the two-dimensional gas formed in tensile-strained Si1-xGex/Si/Si1-xGex heterostructures is investigated using Monte Carlo simulation. At first the electron mobility is studied in ungated modulation doped structures. The calculation matches very well the experimental results over a wide range of electron density. The mobility typically varies between 1100 cm2/Vs in highly-doped structures and 2800 cm2/Vs at low electron density. The mobility is shown to be significantly influenced by the thickness of the spacer layer separating the strained Si channel from the pulse-d…
Using Ginzburg-Landau approach we show that the strain of the nematic superconductor can generate a specific (nematic) vorticity. In the case of doped topological insulators that vorticity forms a spin vortex. We find two types of topologically different spin vortices that either enhance (type I) or suppress (type II) superconductivity far from the vortex core. We apply Bogoliubov-de Geunnes equations to study electronic states in the nematic superconductor with spin vortices. We find that in the case of the vortex of type I, zero-energy states are localized near the vortex core. These states …
We demonstrate the optical addressability of the spin of an individual Chromium atom (Cr) embedded in a semiconductor quantum dot. The emission of Cr-doped quantum dots and their evolution in magnetic field reveal a large magnetic anisotropy of the Cr spin induced by local strain. This results in the zero field splitting of the 0, +-1 and +-2 Cr spin states and in a thermalization on the magnetic ground states 0 and +-1. The observed strong spin to strain coupling of Cr is of particular interest for the development of hybrid spin-mechanical devices where coherent mechanical driving of an indiv…
A split gate technique is used to form a lateral quantum dot in a two-dimensional electron gas of a modulation-doped silicon/silicon-germanium heterostructure. e-beam lithography was employed to produce split gates. By applying negative voltages to these gates the underlying electron gas is depleted and a lateral quantum dot is formed, the size of which can be adjusted by the gate voltage. We observe single-electron operation with Coulomb blockade behavior below 1K. Gate leakage currents are well controlled, indicating that the recently encountered problems with Schottky gates for this type of…
Degenerately doped semiconductor nanocrystals (NCs) exhibit a localized surface plasmon resonance (LSPR) in the infrared range of the electromagnetic spectrum. Unlike metals, semiconductor NCs offer tunable LSPR characteristics enabled by doping, or via electrochemical or photochemical charging. Tuning plasmonic properties through carrier density modulation suggests potential applications in smart optoelectronics, catalysis, and sensing. Here, we elucidate fundamental aspects of LSPR modulation through dynamic carrier density tuning in Sn-doped Indium Oxide NCs. Monodisperse Sn-doped Indium Ox…
It is essential to explore two-dimensional (2D) material with magnetic ordering in new generation spintronic devices. Particularly, the seeking of room-temperature 2D ferromagnetic (FM) materials is a hot topic of current research. Here, we study magnetism of the Mn-doped and electron-doped SiC monolayer using first-principle calculations. For the Mn-doped SiC monolayer, we find that either electron or hole could mediate the ferromagnetism in the system and the Curie temperature ($T_C$) can be improved by appropriate carrier doping. The codoping strategy is also discussed on improving $T_C$. T…
Bismuth-doped Yttrium iron garnet (Bi:YIG) thin films known for large Magneto-optical activity with low losses still needs to get probed for its magnetization dynamics. We demonstrate a controlled tuning of magnetocrystalline anisotropy in Bi-doped Y_3 Fe_5 O_12 (Bi:YIG) films of high crystalline quality using growth induced epitaxial strain on [111]-oriented Gd_3 Ga_5 O_12 (GGG) substrate. We optimize a growth protocol to get thick highly-strained epitaxial films showing large magneto-crystalline anisotropy, compare to thin films prepared using a different protocol. Ferromagnetic resonance me…
Single-pulse strain-induced precessional dynamics of magnetization in Co-doped iron garnet
HFML-FELIX；Radboud University, Institute for Molecules and Materials（拉德堡德大学分子与材料研究所）；Russian Quantum Center, Skolkovo Innovation Center（俄罗斯量子中心斯科尔科沃创新中心）；Faculty of Physics, Lomonosov Moscow State University（莫斯科国立大学物理系）；Faculty of Physics, University of Bialytsok（比亚韦斯托克大学物理系）
On the basis of detailed first-principles calculations the anisotropic thermoelectric transport properties of biaxially strained silicon were studied with focus on a possible enhancement of the powerfactor. Electron as well as hole doping were examined in a broad doping and temperature range. In the low-temperature and low-doping regime an enhancement of the powerfactor was obtained for compressive and tensile strain in the electron-doped case and for compressive strain in the hole-doped case. In the thermoelectrically more important high-temperature and high- doping regime a slight enhancemen…
Graphene superlattices formed by periodic strain are considered theoretically. It is shown that electron energy spectrum consists of minibands obtained by folding of the cone at the boundaries of the superlattice Brillouin zone with very narrow anticrossing regions. Light absorption under direct interminiband transitions is shown to be frequency dependent and dichroic. Giant dichroism of absorption is demonstrated for doped graphene superlattices. Asymmetrical graphene superlattices act as quantum ratchets allowing for generation of photocurrent at absorption of normally incident light. The he…
We report on the coherent dynamics of the spin of an individual magnetic atom coupled to carriers in a semiconductor quantum dot which has been investigated by resonant photoluminescence of the positively charged exciton (X+). We demonstrate that a positively charged CdTe/ZnTe quantum dot doped with a single Mn atom forms an ensemble of optical Lambda systems which can be addressed independently. We show that the spin dynamics of the X+Mn complex is dominated by the electron-Mn exchange interaction and report on the coherent dynamics of the electron-Mn spin system that is directly observed in …
In metal/degenerately doped silicon bilayer structure, the interfacial flexoelectric effect due to strain gradient leads to charge carrier transfer from metal layer to the silicon layer. This excess charge carrier concentration is called flexoelectronic doping or flexoelectronic charge transfer, which gives rise to an electronically polarized (order of magnitude larger than ferroelectric materials) silicon layer. In the transport measurements, the charge carrier concentration in silicon is found to increase by two orders of magnitude due to flexoelectronic doping, which changes the Fermi level…
In this work, we investigate the possibility of enhancing the thermoelectric power (Seebeck coefficient) in graphene devices by strain and doping engineering. While a local strain can result in the misalignment of Dirac cones of different graphene sections in the k-space, doping engineering leads to their displacement in energy. By combining these two effects, we demonstrate that a conduction gap as large as a few hundreds meV can be achieved and hence the enhanced Seebeck coefficient can reach a value higher than 1.4 mV/K in graphene doped heterojunctions with a locally strained area. Such he…
The Andreev conductance across 2d normal metal (N)/superconductor (SC) junctions with relativistic Dirac spectrum is investigated theoretically in the Blonder-Tinkham-Klapwijk formalism. It is shown that for relativistic materials, due to the Klein tunneling instead of impurity potentials, the local strain in the junction is the key factor that determines the transparency of the junction. The local strain is shown to generate an effective Dirac $δ$-gauge field. A remarkable suppression of the conductance are observed as the strength of the gauge field increases. The behaviors of the conductanc…
The spatial distribution of the local density of states (LDOS) at Mn acceptors near the (110) surface of p-doped InAs is investigated by Scanning Tunneling Microscopy (STM). The shapes of the acceptor contrasts for different dopant depths under the surface are analyzed. Acceptors located within the first ten subsurface layers of the semiconductor show a lower symmetry than expected from theoretical predictions of the bulk acceptor wave function. They exhibit a (001) mirror asymmetry. The degree of asymmetry depends on the acceptor atoms' depths. The measured contrasts for acceptors buried belo…
Control of heat flux at small length scales is crucial for numerous solid-state devices and systems. In addition to the thermal management of information and communication devices the mastering of heat transfer channels down to the nanoscale also enable, e.g., new memory concepts, high sensitivity detectors and sensors, energy harvesters and compact solid-state refrigerators. Electronic coolers and thermal detectors for electromagnetic radiation, especially, rely on the maximization of electro-thermal response and blockade of phonon transport. In this work, we propose and demonstrate that effi…
Superconductivity (SC) in the Ba-122 family of iron-based compounds can be controlled by aliovalent or isovalent substitutions, applied external pressure, and strain, the combined effects of which are sometimes studied within the same sample. Most often, the result is limited to a shift of the SC dome to different doping values. In a few cases, the maximum SC transition at optimal doping can also be enhanced. In this work, we study the combination of charge doping together with isovalent P substitution and strain by performing ionic gating experiments on BaFe$_2$(As$_{0.8}$P$_{0.2}$)$_2$ ultra…
Mo$X_2$ ($X$=S or Se) is a semiconductor family with two-dimensional structure. And a recent calculation predicted the superconductivity in electron doped MoS$_2$ monolayer. In this work, the electronic structure and lattice dynamics of Mo$X_2$ bilayers with monolayer Na intercalated, have been calculated. According to the electron-phonon interaction, it is predicted that these bilayers can be transformed from indirect-gap semiconductors to a superconductors by Na intercalation. More interestingly, the biaxial tensile strain can significantly enhance the superconducting temperature up to $\sim…
