7 research outputs found
Anomalous conductivity of -symmetric Fermi liquids
We consider a non-Hermitian yet -symmetric Fermi liquid
(-FL) in external electric fields. Due to
-symmetry, the system exhibits real spectrum, Fermi surface and
electric conductivity are well-defined through propagators. We find that, in
contrast to the conventional Fermi liquids (FL), the -FL can
exhibit a zero resistance state in the longitudinal () channel. Moreover,
the temperature dependence of the resistivity anomaly violates the conventional
FL scaling (it is not limited by ). These findings open route to further
exploration of transport anomalies beyond the conventional paradigm.Comment: 5 pages, 3 figure
Origin of band flatness and constraints of higher Chern numbers
Flat bands provide a natural platform for emergent electronic states beyond
Landau paradigm. Among those of particular importance are flat Chern bands,
including bands of higher Chern numbers (). We introduce a new
framework for band flatness through wave functions, and classify the existing
isolated flat bands in a "periodic table" according to tight binding features
and wave function properties. Our flat band categorization encompasses
seemingly different classes of flat bands ranging from atomic insulators to
perfectly flat Chern bands and Landau Levels. The perfectly flat Chern bands
satisfy Berry curvature condition which
on the tight-binding level is fulfilled only for infinite-range models. Most of
the natural Chern bands fall into category of ; the complexity of creating
higher- flat bands is beyond the current technology. This is due to the
breakdown of the microscopic stability for higher- flatness, seen
atomistically e.g. in the increase of the hopping range bound as
. Within our new formalism, we indicate strategies for
bypassing higher- constraints and thus dramatically decreasing the
implementation complexity
Noise probing of topological band gaps in dispersionless quantum states
We uncover a useful connection between the integrated current noise
and the topological band gap in dispersionless quantum states,
(in units ), where is the Chern number,
is electric charge, and is the topological band gap. This
relationship may serve as a working principle for a new experimental probe of
topological band gaps in flat band materials. Possible applications include
moir\'e systems, such as twisted bilayer graphene and twisted transition metal
dichalcogenides, where a band gap measurement in meV regime presents an
experimental challenge
Unconventional superfluidity and quantum geometry of topological bosons
We investigate superfluidity of bosons in gapped topological bands and
discover a new phase that has no counterparts in the previous literature. This
phase is characterized by a highly unconventional modulation of the order
parameter, breaking the crystallographic symmetry, and for which the
condensation momentum is neither zero nor any other high-symmetry vector of the
Brillouin zone. This unconventional structure impacts the spectrum of
Bogoliubov excitations and, consequently, the speed of sound in the system.
Even in the case of perfectly flat bands, the speed of sound and Bogoliubov
excitations remain nonvanishing, provided that the underlying topology and
quantum geometry are nontrivial. Furthermore, we derive detailed expressions
for the superfluid weight using the Popov hydrodynamic formalism for
superfluidity and provide estimates for the Berezinskii-Kosterlitz-Thouless
temperature, which is significantly enhanced by the nontriviality of the
underlying quantum metric. These results are applicable to generic topological
bosonic bands, with or without dispersion. To illustrate our findings, we
employ the Haldane model with a tunable bandwidth, including the narrow
lowest-band case. Within this model, we also observe a re-entrant superfluid
behavior: As the Haldane's magnetic flux is varied, the
Berezinskii-Kosterlitz-Thouless transition temperature initially decreases to
almost zero, only to resurface with renewed vigor.Comment: 23 pages, 10 figure
Re-entrant magic-angle phenomena in twisted bilayer graphene in integer magnetic fluxes
In this work we address the re-entrance of magic-angle phenomena (band
flatness and quantum-geometric transport) in twisted bilayer graphene (TBG)
subjected to strong magnetic fluxes , , ... ( is the flux quantum per moir\'e cell). The moir\'e
translation invariance is restored at the integer fluxes, for which we
calculate the TBG band structure using accurate atomistic models with lattice
relaxations. Similarly to the zero-flux physics outside the magic angle
condition, the reported effect breaks down rapidly with the twist. We conclude
that the magic-angle physics re-emerges in high magnetic fields, witnessed by
the appearance of flat electronic bands distinct from Landau levels, and
manifesting non-trivial quantum geometry. We further discuss the possible
flat-band quantum geometric contribution to the superfluid weight in strong
magnetic fields (28 T at 1.08 twist), according to Peotta-T\"{o}rm\"{a}
mechanism.Comment: 5 pages, 5 figure
Engineering SYK interactions in disordered graphene flakes under realistic experimental conditions
We model SYK (Sachdev-Ye-Kitaev) interactions in disordered graphene flakes
up to 300 000 atoms (100 nm in diameter) subjected to an out-of-plane
magnetic field of 5-20 Tesla within the tight-binding formalism. We
investigate two sources of disorder: (i) irregularities at the system
boundaries, and (ii) bulk vacancies, -- for a combination of which we find
conditions which could be favorable for the formation of the phase with SYK
features under realistic experimental conditions above the liquid helium
temperature.Comment: 6 pages, 4 figure