19 research outputs found
Quantization of entropy in a quasi-two-dimensional electron gas
We demonstrate that the partial entropy of a two-dimensional electron gas
(2DEG) exhibits quantized peaks at resonances between the chemical potential
and electron levels of size quantization. In the limit of no scattering, the
peaks depend only on the subband quantization number and are independent on
material parameters, shape of the confining potential, electron effective mass
and temperature. The quantization of partial entropy is a signature of a
topological phase transition in a 2DEG. In the presence of stationary disorder,
the magnitude of peaks decreases. Its deviation from the quantized values is a
direct measure of the disorder induced smearing of the electronic density of
states.Comment: 4 pages, 2 figure
The Ferromagnetism in the Vicinity of Lifshitz Topological Transitions
We show that the critical temperature of a ferromagnetic phase transition in
a quasi-two-dimensional hole gas confined in a diluted magnetic semiconductor
quantum well strongly depends on the hole chemical potential and hole density.
The significant variations of the the Curie temperature occur close to the
Lifshitz topological transition points where the hole Fermi surface acquires
additional components of topological connectivity due to the filling of excited
size-quantization subbands. The model calculations demonstrate that the Curie
temperature can be doubled by a small variation of the gate voltage for the
CdMnTe/CdMgTe quantum well based device
Proposed Model of the Giant Thermal Hall Effect in Two-Dimensional Superconductors: An Extension to the Superconducting Fluctuations Regime
We extend the thermodynamic approach for the description of the thermal Hall
effect in the vicinity of a superconducting phase transition, in the
fluctuation dominated regime. We show that the Hall heat conductivity is
proportional to the product of temperature derivatives of the chemical
potential and of the magnetization of the system. We argue that the latter
derivative shows the strong singularity in the vicinity of the phase
transition, while the former does not contain the characteristic for fermionic
systems smallness (T /EF ), what additionally increases the effect. We derive
the analytical formula predicting the temperature dependence of the thermal
Hall conductivity in the vicinity of the critical temperature for different
magnetic fields. Moreover, we study the phenomenon in the regime of quantum
fluctuations, in the vicinity of the second critical field and at very low
temperatures. We demonstrate how it fades away in a full agreement with the
third law of thermodynamics. The developed approach qualitatively explains the
recently observed giant thermal Hall effect in cuprates [1].Comment: 5 pages, 2 figure
Detection of topological phase transitions through entropy measurements: the case of germanene
We propose a characterization tool for studies of the band structure of new
materials promising for the observation of topological phase transitions. We
show that a specific resonant feature in the entropy per electron dependence on
the chemical potential may be considered as a fingerprint of the transition
between topological and trivial insulator phases. The entropy per electron in a
honeycomb two-dimensional crystal of germanene subjected to the external
electric field is obtained from the first principle calculation of the density
of electronic states and the Maxwell relation. We demonstrate that, in
agreement to the recent prediction of the analytical model, strong spikes in
the entropy per particle dependence on the chemical potential appear at low
temperatures. They are observed at the values of the applied bias both below
and above the critical value that corresponds to the transition between the
topological insulator and trivial insulator phases, while the giant resonant
feature in the vicinity of zero chemical potential is strongly suppressed at
the topological transition point, in the low temperature limit. In a wide
energy range, the van Hove singularities in the electronic density of states
manifest themselves as zeros in the entropy per particle dependence on the
chemical potential.Comment: 8 pages, 5 figures; final version published in PR