We report on a study of electronic transport in semi-metallic Bi$_{0.96}$Sb$_{0.04}$. At zero field, the system is a very dilute Fermi liquid displaying a T$^{2}$ resistivity with an enhanced prefactor. Quantum oscillations in resistivity as well as in Hall, Nernst and Seebeck responses of the system are detectable and their period quantifies the shrinking of the Fermi surface with antimony doping. For a field along the trigonal axis, the quantum limit was found to occur at a field as low as 3T. An ultraquantum anomaly at twice this field was detected in both charge transport and Nernst response. Its origin appears to lie beyond the one-particle picture and linked to unidentified many-body effects.
We report on the synthesis and transport properties of perovskite (Pv) CaIrO3 thin films. The Pv phase of CaIrO3 was stabilized by epitaxial growth on SrTiO3, (LaAlO3)0.3(Sr2AlTaO6)0.7, and LaAlO3 substrates with strong tensile, weak tensile, and compressive strains, respectively. The resistivity of these films showed a poorly metallic behavior. The Hall resistivity exhibited a sign change as a function of temperature and a nonlinear magnetic-field dependence, which clearly indicated the coexistence of electrons and holes and hence supported that Pv CaIrO3 films are semimetallic. The observed …
Magnetoresistance in single crystals of black phosphorus is studied at ambient and hydrostatic pressures. In the semiconducting states at pressures below 0.71 GPa, the magnetoresistance shows periodic oscillations, which can be ascribed to the magneto-phonon resonance that is characteristic of high mobility semiconductors. In the metallic state above 1.64 GPa, the both transverse and longitudinal magnetoresistance show titanic increase with exhibiting superposed Shubnikov-de Haas oscillations. The observed small Fermi surfaces, high mobilities and light effective masses of carriers in semimeta…
We report on the electronic transport properties of black phosphorus and analyze them using a two-carrier model in a wide range of pressure up to 2.5 GPa. In semiconducting state at 0.29 GPa, the remarkable non-linear behavior in the Hall resistance is reasonably reproduced by assuming the coexistence of two kinds of hole with different densities and mobilities. On the other hand, two-carrier analyses of the magnetotransport properties above 1.01 GPa suggest the coexistence of high mobility electron and hole carriers that have almost the same densities, i.e., nearly compensated semimetallic na…
Pt-induced semimetallic transport and enhanced thermoelectric response in the half-Heusler alloy YNi_{0.5}Pt_{0.5}Bi
Indian Institute of Technology Delhi（印度德里理工学院）；Harbin Institute of Technology（哈尔滨工业大学）；Chalmers University of Technology（查尔姆斯理工大学）；Damanhour University（达曼胡尔大学）；Max-Planck-Institut für Chemische Physik fester Stoffe（马克斯·普朗克固体化学物理研究所）；Tohoku University（东北大学）
$α$-(BEDT-TTF)$_2$I$_3$ is a prominent example of charge ordering among organic conductors. In this work we explore the details of transport within the charge-ordered as well as semimetallic phase at ambient pressure. In the high-temperature semimetallic phase, the mobilities and concentrations of both electrons and holes conspire in such a way to create an almost temperature-independent conductivity as well as a low Hall effect. We explain these phenomena as a consequence of a predominantly inter-pocket scattering which equalizes mobilities of the two types of charge carriers. At low temperat…
From measurements of fluctuation spectroscopy and weak nonlinear transport on the semimetallic ferromagnet EuB$_6$ we find direct evidence for magnetically-driven electronic phase separation consistent with the picture of percolation of magnetic polarons (MP), which form highly conducting magnetically-ordered clusters in a paramagnetic and 'poorly conducting' background. These different parts of the conducting network are probed separately by the noise spectroscopy/nonlinear transport and the conventional linear resistivity. We suggest a comprehensive and 'universal' scenario for the MP percol…
Metals with values of the resistivity and the Hall coefficient much larger than typical ones, e.g., of sodium, are called semimetals. We suggest a model for semimetals which takes into account the strong Coulomb repulsion of the charge carriers, especially important in transition-metal and rare-earth compounds. For that purpose we extend the Hubbard model by coupling one additional orbital per site via hybridization to the Hubbard orbitals. We calculate the spectral function, resistivity and Hall coefficient of the model using dynamical mean-field theory. Starting from the Mott-insulating stat…
We report measurements of weakly nonlinear electronic transport, as measured by third-harmonic voltage generation $V_{3ω}$, in the low-carrier density semimetallic ferromagnet EuB$_6$, which exhibits an unusual magnetic ordering with two consecutive transitions at $T_{c_1} = 15.6$\,K and $T_{c_2} = 12.5$\,K. Upon cooling in zero magnetic field through the ferromagnetic transition, the dramatic drop in the linear resistivity at the upper transition $T_{c_1}$ coincides with the onset of nonlinearity, and upon further cooling is followed by a pronounced peak in $V_{3 ω}$ at the lower transition $…
The low-temperature transport properties (resistivity, thermal conductivity, thermoelectric power) are experimentally investigated for the compound YbMn2Sb2. Large Seebeck coefficient and nearly linear temperature dependence of resistivity are obtained. The thermal conductivity is large and has mainly phonon origin. Appreciable anomalies of transport characteristics near the antiferromagnetic transition point are found. Possible influence of pseudo-Kondo scattering is discussed.
We report that the surface conductivity of Na$_{2}$IrO$_3$ crystal is extremely tunable by high energy Ar plasma etching and can be tuned from insulating to metallic with increasing etching time. Temperature dependent electrical transport for the metallic samples show signatures of first order phase transitions which are consistent with charge or spin density wave like phase transitions recently predicted theoretically. Additionally, grazing-incidence small-angle x-ray scattering (GISAXS) reveal that the room temperature surface structure of Na$_{2}$IrO$_3$ does not change after plasma etching…
Magnetic topological semimetals have attracted intense attention recently since these materials carry a great promise for potential applications in novel spintronic devices. Here, we report an intimate interplay between lattice, Eu magnetic order and topological semimetallic behavior in Eu$_{1-x}$Sr$_{x}$MnSb$_{2}$ driven by nonmagnetic Sr doping on magnetic Eu site. Different types of Eu spin reorientations are controllable by the Sr concentration, temperature or magnetic field, and coupled to the quantum transport properties of Dirac fermions generated by the 2D Sb layers. Our study opens a …
We discuss the transport anomalies associated with the development of heavy electrons out of a neutral spin fluid using the large-N treatment of the Kondo-Heisenberg lattice model. At the phase transition in this model the spin excitations suddenly acquire charge. The Higgs process by which this takes place causes the constraint gauge field to loosely ``lock'' together with the external, electromagnetic gauge field. From this perspective, the heavy fermion phase is a Meissner phase in which the field representing the difference between the electromagnetic and constraint gauge field, is exclude…
We report a layered ternary selenide BaPt4Se6 featuring sesqui-selenide Pt2Se3 layers sandwiched by Ba atoms. The Pt2Se3 layers in this compound can be derived from the Dirac-semimetal PtSe2 phase with Se vacancies that form a honeycomb structure. This structure results in a Pt (VI) and Pt (II) mixed-valence compound with both PtSe6 octahedra and PtSe4 square net coordination configurations. Temperature dependent electrical transport measurements suggest two distinct anomalies: a resistivity crossover, mimic to the metal-insulator (M-I) transition at ~150K, and a resistivity plateau at tempera…
The results of magnetization, heat-capacity, and electrical resistivity (rho) studies of the compounds, RMAs2 (R= Pr and Sm; M= Ag, Au), crystallizing in HfCuSi2-derived structure are reported. PrAgAs2 orders antiferromagnetically at T_N= 5 K. The Au analogue, however, does not exhibit long range magnetic order down to 1.8 K. We infer that this is due to subtle differences in their crystallographic features, particularly noting that both the Sm compounds with identical crystal structure as that of former order magnetically nearly at the same temperature (about 17 K). It appears that, in PrAgAs…
The results of dc magnetization, heat capacity, electrical resistivity (rho) and magnetoresistance measurements are reported in detail for the compounds, RCuAs2 for R= Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er, crystallizing in HfCuSi2-type tetragonal structure, with the aim of bringing out anomalies among 'normal' (that is, other than Ce and Yb) rare-earths. The results establish that all these compounds order antiferromagnetically at low temperatures with deviations from de Gennes scaling. Isothermal magnetization (M) data below respective Neel temperatures (TN) reveal the existence of field-induce…
The drastic changes of Fermi surfaces as well as transport anomalies near P=Pc~2.35 GPa in CeRhIn5 are explained theoretically from the viewpoint of sharp valence change of Ce. It is pointed out that the key mechanism is the interplay of magnetic order and Ce-valence fluctuations. It is shown that the antiferromagnetic state with "small" Fermi surfaces changes to the paramagnetic state with "large" Fermi surfaces with huge enhancement of effective mass of electrons with keeping finite c-f hybridization. This naturally explains the de Haas-van Alphen measurement and also the transport anomalies…
In this paper we study transport properties of electrons on the two-dimensional honeycomb lattice. We consider a half-filled system in the vicinity of a symmetry-breaking transition from a semimetallic phase towards an insulating phase with either charge density or spin density wave order. The effect of either order is to break the sublattice inversion symmetry which induces a finite gap for the electronic single-particle excitations. Phenomenologically, such a scenario is described in the framework of a Gross-Neveu theory. We analyze two related formulations of the model by means of (i) a con…
Kondo insulating materials lie outside the usual dichotomy of weakly versus correlated - band versus Mott - insulators. They are metallic at high temperatures but resemble band insulators at low temperatures because of the opening of an interaction induced band gap. The first discovered Kondo insulator (KI) SmB$_6$ has been predicted to form a topological KI (TKI) which mimics a topological insulator at low temperatures. However, since its discovery thermodynamic and transport anomalies have been observed that have defied a theoretical explanation. Enigmatic signatures of collective modes insi…
The strange metal phase of optimally and overdoped cuprates exhibits a number of anomalous transport properties: unsaturating linear T resistivity, distinct relaxation times for Hall angle and resistivity, temperature dependent anisotropic relaxation times, and a characteristic crossover from supposed Fermi Liquid to linear T behavior. All receive natural explanations and quantitative fits in terms of the Hidden Fermi Liquid theory.
The behavior of the conductivity and the density of states, as well as the phase relaxation time, of disordered itinerant electrons across a quantum ferromagnetic transition is discussed. It is shown that critical fluctuations lead to anomalies in the temperature and energy dependence of the conductivity and the tunneling density of states, respectively, that are stronger than the usual weak-localization anomalies in a disordered Fermi liquid. This can be used as an experimental probe of the quantum critical behavior. The energy dependence of the phase relaxation time at criticality is shown t…
The mechanism of drastic change of Fermi surfaces as well as transport anomalies near P=Pc=2.35 GPa in CeRhIn5 is explained theoretically. The key mechanism is pointed out to be the interplay of magnetic order and Ce-valence fluctuations. We show that the antiferromagnetic state with "small" Fermi surfaces changes to the paramagnetic state with "large" Fermi surfaces with huge enhancement of effective mass of electrons with keeping finite c-f hybridization. This explains the drastic change of the de Haas-van Alphen signals. Furthermore, it is also consistent with the emergence of T-linear resi…
We have carried out magnetization, heat capacity, electrical and magnetoresistance measurements (2-300 K) for the polycrystalline form of intermetallic compounds, R2RhSi3 (R= Gd, Tb, and Dy), forming in a AlB2 derived hexagonal structure with a triangular R network. This work was primarily motivated by a revival of interest on Gd2PdSi3 after about two decades in the field of Toplogical Hall Effect due to magnetic skyrmions. We report here that these compounds are characterized by double antiferromagnetic transitions (T_N= 13.5 and 12 K for Gd, 13.5 and 6.5 K for Tb; 6.5 and 2.5 for Dy), but an…
A shallow potential well in a near-perfect quantum wire will bind a single-electron and behave like a quantum dot, giving rise to spin-dependent resonances of propagating electrons due to Coulomb repulsion and Pauli blocking. It is shown how this may be used to generate full entanglement between static and flying spin-qubits near resonance in a two-electron system via singlet or triplet spin-filtering. In a quantum wire with many electrons, the same pairwise scattering may be used to explain conductance, thermopower and shot-noise anomalies, provided the temperature/energy scale is sufficientl…
Superconductivity research is like running a marathon. Three decades after the discovery of high-Tc cuprates, there have been mass data generated from transport measurements, which bring fruitful information. In this review, we give a brief summary of the intriguing phenomena reported in electron-doped cuprates from the aspect of electrical transport as well as the complementary thermal transport. We attempt to sort out common features of the electron-doped family, e.g. the strange metal, negative magnetoresistance, multiple sign reversals of Hall in mixed state, abnormal Nernst signal, comple…
Transport studies seem to be one of the strongest lines of support for a preformed pair approach to the pseudogap. In this paper we provide a fresh, physically transparent look at two important quantities: the diamagnetic susceptibility and conductivity. We use a three dimensional preformed pair framework which has had some success in the cold Fermi gases and in the process we reconcile recently observed inconsistencies. Specifically, while the preformed pairs in our theory give a large contribution to the diamagnetic susceptibility, the imaginary part of the conductivity is suppressed to zero…
The conductivity and the tunneling density of states of disordered itinerant electrons in the vicinity of a ferromagnetic transition at low temperature are discussed. Critical fluctuations lead to nonanalytic frequency and temperature dependences that are distinct from the usual long-time tail effects in a disordered Fermi liquid. The crossover between these two types of behavior is proposed as an experimental check of recent theories of the quantum ferromagnetic critical behavior. In addition, the quasiparticle properties at criticality are shown to be those of a marginal Fermi liquid.
Chiral anomalies have profound impact on the transport properties of relativistic fluids. In four dimensions there are different types of anomalies, pure gauge and mixed gauge-gravitational anomalies. They give rise to two new non-dissipative transport coefficients, the chiral magnetic conductivity and the chiral vortical conductivity. They can be calculated from the microscopic degrees of freedom with the help of Kubo formulae. We review the calculation of the anomalous transport coefficients via Kubo formulae with a particular emphasis on the contribution of the mixed gauge-gravitational ano…
Quantum transport simulations are rapidly evolving and now encompass well-controlled tensor network techniques for many-body limits. One powerful approach combines matrix product states with extended reservoirs. In this method, continuous reservoirs are represented by explicit, discretized counterparts and a chemical potential or temperature drop is maintained by external relaxation. Currents are strongly influenced by relaxation when it is very weak or strong, resulting in a simulation analog of Kramers' turnover for solution-phase chemical reactions. At intermediate relaxation, the intrinsic…
We revisit the study of a 2D quantum field theory in the hydrodynamic regime and develop a formalism based on Euclidean one-loop partition functions that is suitable to analyze transport properties due to gauge and gravitational anomalies. To do so, we generalize the method of a modified Dirac operator developed for zero-temperature anomalies to finite temperature, chemical potentials and rotations.
Finite-temperature ($T$) properties of a Kitaev model defined on a honeycomb lattice are investigated by a quantum Monte Carlo simulation, from the viewpoint of fractionalization of quantum $S=1/2$ spins into two types of Majorana fermions, itinerant and localized. In this system, the entropy is released successively at two well-separated $T$ scales, as a clear indication of the thermal fractionalization. We show that the high-$T$ crossover, which is driven by itinerant Majorana fermions, is closely related with the development of nearest-neighbor spin correlations. On the other hand, the low-…
We present results of electrical resistivity, magnetoresistance and ac and dc magnetic susceptibility on polycrystalline samples of the type La(0.5)Ca(0.5-x)Ba(x)MnO(3) synthesized under identical heat treatment conditions. The substitution of larger Ba ions for Ca results in a non- monotonic variation of the curie temperature as the system evolves from a charge ordered insulating state for x=0 to a ferromagnetic metallic state for x=0.5. An intermediate compositino, x=0.1, interestingly exhibits ferromagnetic. insulating behaviour with thermal hysteresis in ac chi around the curie tem- peratu…
Quantum anomalies are one of the subtlest properties of relativistic field theories. They give rise to non-dissipative transport coefficients in the hydrodynamic expansion. In particular a magnetic field can induce an anomalous current via the chiral magnetic effect. In this work we explore the possibility that anomalies can induce a chiral magnetic effect in non-anomalous currents as well. This effect is implemented through an explicit breaking of the symmetries.
Specific d-wave angular dependence of the in-plane magnetoresistence in antiferromagnetic tetragonal YBa_{2}Cu_{3}O_{6+x} (x~0.3) on orientation of the external magnetic field in (a,b) plane is assigned to the effective hole transport through low lying excited purely oxygen doublet O2pe_u state, not the ground b_{1g}(d_{x^2-y^2}) state. External magnetic field determines the orientation of the strong exchange field for the spin-triplet b_{1g}e_u:{}^{3}E_u state of the hole CuO_4 center and due to the spin-orbital coupling results in either orbital polarization of the E_u doublet giving rise to…
Quantum anomalies give rise to new non-dissipative transport phenomena in relativistic fluids induced by external electromagnetic fields and vortices. These phenomena can be studied in holographic models with Chern-Simons couplings dual to anomalies in field theory. We perform a computation in AdS/CFT of the anomalous transport coefficients in a holographic massive gravity model, and find that the anomalous conductivities turn out to be independent of the holographic disorder couplings of the model. To arrive at this result we suggest a new definition of the energy-momentum tensor in presence …
The effective low-energy excitations in a metallic or semimetallic crystalline system (i.e. electronic quasiparticles) always have a finite spatial extent. It is self-evident but virtually unexplored how the associated internal degrees of freedom manifest themselves in the quasiparticle response. Here, we investigate this question by illuminating an intimate connection between the theory of nonlinear response and the equations of motion of classical deformable bodies. This connection establishes that nth-order response in an external perturbation corresponds to nth-order derivatives of the qua…
We report the results of magnetic, heat-capacity, electrical and magnetoresistance measurements on Ho4RhAl and Er4RhAl, characterized by 3 sites for rare-earths (R). Antiferromagnetic ordering sets in at (T_N =) about 8.8 and 4.0 K respectively. While Ho compound appears to enter into a complex spin-glass phase at T less thanT_N (at nearly 5 K), spin-glass component appears to set in essentially almost at T_N for the Er case. The loss of the spin-disorder contribution in the magnetically ordered state is not pronounced, mimicking that in Gd2PdSi3, a compound which now attracts interest in the …
We investigated the nature of transport and magnetic properties in SrIr0.5Ru0.5O3, (SIRO) which has characteristics intermediate between a correlated non-Fermi liquid state and an itinerant Fermi liquid state, by growing perovskite thin films on various substrates (SrTiO3 (001), (LaAlO3)0.3(Sr2TaAlO6)0.7 (001) and LaAlO3 (001)). We observed systematic variation of underlying substrate dependent metal-to-insulator transition temperatures at 80 K on SrTiO3, 90 K on (LaAlO3)0.3(Sr2TaAlO6)0.7 and 100 K on LaAlO3) in resistivity. Resistivity in the metallic region follows a T3/2 power law; whereas …
Relativistic gravitational anomalies lead to anomalous transport coefficients that can be activated at finite temperature in condensed matter systems with gapless fermions. The chiral vortical effect (CVE) is an anomalous chiral current along a rotation axis, expressed in terms of a gravimagnetic field and a gravitational anomaly. Another one, the chiral torsional effect (CTE), arises from hydrodynamically independent frame fields and connection. We discuss the relation of CVE, CTE and gravitational anomalies for relativistic fermions from the perspective of torsion and the Nieh-Yan anomaly. T…
We argue that an effective field theory of local fluid elements captures the constraints on hydrodynamic transport stemming from the presence of quantum anomalies in the underlying microscopic theory. Focussing on global current anomalies for an arbitrary flavour group, we derive the anomalous constitutive relations in arbitrary even dimensions. We demonstrate that our results agree with the constraints on anomaly governed transport derived hitherto using a local version of the second law of thermodynamics. The construction crucially uses the anomaly inflow mechanism and involves a novel therm…
