arXiv subjects

L. V. Butov

Publications and source records attributed to L. V. Butov.

At least 19 recordsLinked to original sources

arXiv2026

Excitonic pattern formation from a wrinkling instability in a van der Waals heterostructure

We studied photoluminescence of spatially indirect excitons (IXs) in a MoSe$_2$/WSe$_2$ van der Waals heterostructure. We observed a quasi-periodic triangular pattern of IXs with a characteristic spatial wavelength $\sim{}2.6\,μ\mathrm{m}$. Our theoretical analysis using a Föppl-von Kármán theory finds an elastic instability that produces triangular patterns with micrometer-scale wavelengths. This mechanism is consistent with the wavelength, symmetry, excitation power dependence, and temperature dependence of the observed IX pattern.

cond-mat.mes-hall↗

arXiv2026

Efficient transport kinetics of indirect excitons in van der Waals heterostructure

Exciton transport is fundamental for understanding transport phenomena in bosonic systems and for exploring excitation energy transfer in materials. Spatially indirect excitons (IXs) have long lifetimes allowing them to form quantum bosonic states and travel long distances. Van der Waals heterostructures form a new materials platform for exploring IX transport. Disordered in-plane potentials suppress IX transport due to IX localization and scattering. In this work, we found the efficient IX transport kinetics characterized by anomalously high IX mobility. The efficient IX transport kinetics is observed in the presence of in-plane disorder and is consistent with predicted IX superfluidity.

cond-mat.mes-hall↗

arXiv2026

Transport of indirect excitons and exciton mediated spin transport in a van der Waals heterostructure in magnetic fields

We studied transport of indirect excitons (IXs) and IX mediated spin transport in a MoSe$_2$/WSe$_2$ van der Waals heterostructure in magnetic fields up to 8 T. We observed the long-range IX transport and the long-range IX mediated spin transport in the magnetic fields. The IX transport and spin transport are characterized by the 1/e decay distances reaching $\sim$ 100 micrometers. The decay distance of the spin transport correlates with the decay distance of IX transport. These decay distances first increase and then decrease with increasing IX density for all studied magnetic fields. The long-range IX transport and the long-range spin transport in the magnetic fields are consistent with the similar long-range transport in zero magnetic field.

cond-mat.mes-hall↗

arXiv2025

Interference dislocations adjacent to emission spot

We studied interference dislocations (forks) adjacent to an emission spot in an interference pattern. The adjacent interference dislocations are observed in emission of excitons in a monolayer transition metal dichalcogenide and in emission of spatially indirect excitons, also known as interlayer excitons, in a van der Waals heterostructure. The simulations show that the adjacent interference dislocations appear due to the moiré effect in combined interference patterns produced by constituting parts of the emission spot. The adjacent interference dislocations can appear in interference images for various spatially modulated emission patterns.

cond-mat.mes-hall↗

arXiv2025

Long-range spatial extension of exciton states in van der Waals heterostructure

Narrow lines in photoluminescence (PL) spectra of excitons are characteristic of low-dimensional semiconductors. These lines correspond to the emission of exciton states in local minima of a potential energy landscape formed by fluctuations of the local exciton environment in the heterostructure. The spatial extension of such states was in the nanometer range. In this work, we present studies of narrow lines in PL spectra of spatially indirect excitons (IXs) in a MoSe$_2$/WSe$_2$ van der Waals heterostructure. The narrow lines vanish with increasing IX density. The disappearance of narrow lines correlates with the onset of IX transport, indicating that the narrow lines correspond to localized exciton states. The narrow lines extend over distances reaching several micrometers and over areas reaching ca. ten percent of the sample area. This macroscopic spatial extension of the exciton states, corresponding to the narrow lines, indicates a deviation of the exciton energy landscape from random potential and shows that the excitons are confined in moiré potential with a weak disorder.

cond-mat.mes-hall↗

arXiv2025

Mott transition in excitonic Bose polarons

For a neutral system of positive and negative charges, such as atoms in a crystal, increasing the density causes the Mott transition from bound electrons to free electrons. The density of optically generated electron-hole systems can be controlled in situ by the power of optical excitation that enables the Mott transition from excitons, the bound pairs of electrons and holes, to free electrons and holes with increasing density. These Mott transitions occur in systems of pairs of the same kind, such as atoms or excitons. However, a different type of the Mott transition can occur for Bose polarons. A Bose polaron is a mobile particle of one kind in a Bose gas of particles of another kind. For the Mott transition in polarons, the polaron states vanish with increasing density of the surrounding gas. In this paper, we present the observation of this type of the Mott transition and the measurement of the Mott transition parameter $n_{\rm M}^{1/2} a_{\rm B}$ in 2D excitonic Bose polarons.

cond-mat.quant-gas↗

arXiv2024

Excitonic Bose-polarons in electron-hole bilayers

Bose polarons are mobile impurities dressed by density fluctuations of a surrounding degenerate Bose gas. These many-body objects have been realized in ultracold atomic gasses and become a subject of intensive studies. In this work, we show that excitons in electron-hole bilayers offer new opportunities for exploring polarons in strongly interacting, highly tunable bosonic systems. We found that Bose polarons are formed by spatially direct excitons immersed in degenerate Bose gases of spatially indirect excitons (IXs). We detected both attractive and repulsive Bose polarons by measuring photoluminescence excitation spectra. We controlled the density of IX Bose gas by optical excitation and observed an enhancement of the energy splitting between attractive and repulsive Bose polarons with increasing IX density, in agreement with our theoretical calculations.

cond-mat.quant-gas↗

arXiv2024

Long-distance decay-less spin transport in indirect excitons in a van der Waals heterostructure

In addition to its fundamental interest, the long-distance spin transport with suppressed spin losses is essential for spintronic devices. However, the spin relaxation caused by scattering of the particles carrying the spin, limits the spin transport. We explored spatially indirect excitons (IXs), also known as interlayer excitons, in van der Waals heterostructures (HS) composed of atomically thin layers of transition-metal dichalcogenides (TMD) as spin carries. TMD HS also offer coupling of spin and valley transport. We observed the long-distance spin transport with the decay distances exceeding 100~$μ$m and diverging so spin currents show no decay in the HS. With increasing IX density, we observed spin localization, then long-distance spin transport, and then reentrant spin localization, in agreement with the Bose-Hubbard theory prediction for superfluid and insulating phases in periodic potentials due to moiré superlattices. The suppression of scattering in exciton superfluid suppresses the spin relaxation and enables the long-distance spin transport. This mechanism of protection against the spin relaxation makes IXs a platform for the realization of long-distance decay-less spin transport.

cond-mat.mes-hall↗

arXiv2023

Transport and localization of indirect excitons in a van der Waals heterostructure

Long lifetimes of spatially indirect excitons (IXs), also known as interlayer excitons, allow implementing both quantum exciton systems and long-range exciton transport. Van der Waals heterostructures (HS) composed of atomically thin layers of transition-metal dichalcogenides (TMD) offer the opportunity to explore IXs in moiré superlattices. The moiré IXs in TMD HS form the materials platform for exploring the Bose-Hubbard physics and superfluid and insulating phases in periodic potentials. IX transport in TMD HS was intensively studied and diffusive IX transport with $1/e$ decay distances $d_{1/e}$ up to $\sim 3$ $μ$m was realized. In this work, we present in MoSe$_2$/WSe$_2$ HS the IX long-range transport with $d_{1/e}$ exceeding 100 $μ$m and diverging at the optical excitation resonant to spatially direct excitons. The IX long-range transport vanishes at high temperatures. With increasing IX density, IX localization, then IX long-range transport, and then IX reentrant localization is observed. The results are in qualitative agreement with the Bose-Hubbard theory of bosons in periodic potentials predicting superfluid at $N \sim 1/2$ and insulating at $N \sim 0$ and $N \sim 1$ phases for the number of bosons per site of the periodic potential $N$.

cond-mat.mes-hall↗

arXiv2022

Fermi edge singularity in neutral electron-hole system

In neutral dense electron-hole (e-h) systems at low temperatures, theory predicts Cooper-pair-like excitons at the Fermi energy and a BCS-like exciton condensation. Optical excitation allows creating e-h systems with the densities controlled by the excitation power. However, the intense optical excitations required to achieve high densities cause substantial heating of the e-h system that prevents the realization of dense and cold e-h systems in conventional semiconductors. In this work, we study e-h systems created by optical excitation in separated electron and hole layers. The layer separation increases the e-h recombination time and, in turn, the density for a given optical excitation by orders of magnitude and, as a result, enables the realization of the dense and cold e-h system. We found a strong enhancement of photoluminescence intensity at the Fermi energy of the neutral dense ultracold e-h system that evidences the emergence of excitonic Fermi edge singularity due to the Cooper-pair-like excitons at the Fermi energy.

cond-mat.quant-gas↗

arXiv2022

Long-range quantum transport of indirect excitons in van der Waals heterostructure

Long lifetimes of spatially indirect excitons (IXs), also known as interlayer excitons, make possible long-range IX propagation. Van der Waals heterostructures composed of atomically thin layers of transition-metal dichalcogenides (TMDs) give an opportunity to realize excitons with high binding energies and provide a materials platform for the realization of both excitonic quantum phenomena and excitonic devices. Propagation of IXs in TMD heterostructures is intensively studied. However, in spite of long IX lifetimes, orders of magnitude longer than lifetimes of spatially direct excitons (DXs), a relatively short-range IX propagation with the $1/e$ decay distances $d_{1/e}$ up to few $μ$m was reported in the studies of TMD heterostructures. The short-range of IX propagation originates from in-plane potentials, which localize excitons and suppress exciton transport. In particular, significant in-plane moiré potentials predicted in TMD heterostructures can cause an obstacle for IX propagation. In this work, we realize in a MoSe$_2$/WSe$_2$ heterostructure a macroscopically long-range IX propagation with $d_{1/e}$ reaching $\sim 100$ $μ$m. The strong enhancement of IX propagation is realized using an optical excitation resonant to DXs in the heterostructure. The strong enhancement of IX propagation originates from the suppression of IX localization and scattering and is observed in the quantum regime.

cond-mat.mes-hall↗

arXiv2021

Voltage-controlled long-range propagation of indirect excitons in van der Waals heterostructure

Indirect excitons (IXs), also known as interlayer excitons, can form the medium for excitonic devices whose operation is based on controlled propagation of excitons. A proof of principle for excitonic devices was demonstrated in GaAs heterostructures where the operation of excitonic devices is limited to low temperatures. IXs in van der Waals transition-metal dichalcogenide (TMD) heterostructures are characterized by high binding energies making IXs robust at room temperature and offering an opportunity to create excitonic devices operating at high temperatures suitable for applications. However, a characteristic feature of TMD heterostructures is the presence of moiré superlattice potentials, which are predicted to cause modulations of IX energy reaching tens of meV. These in-plane energy landscapes can lead to IX localization, making IX propagation fundamentally different in TMD and GaAs heterostructures and making uncertain if long-range IX propagation can be realized in TMD heterostructures. In this work, we realize long-range IX propagation with the $1/e$ IX luminescence decay distances reaching 13 microns in a MoSe$_2$/WSe$_2$ heterostructure. We trace the IX luminescence along the IX propagation path. We also realize control of the long-range IX propagation: the IX luminescence signal in the drain of an excitonic transistor is controlled within 40 times by gate voltage. These data show that the long-range IX propagation is possible in TMD heterostructures with the predicted moiré superlattice potentials.

cond-mat.mes-hall↗

arXiv2019

Localized bright luminescence of indirect excitons and trions in MoSe$_2$/WSe$_2$ van der Waals heterostructure

Indirect excitons (IX) in semiconductor heterostructures are bosons, which can cool below the temperature of quantum degeneracy and can be effectively controlled by voltage and light. IX quantum Bose gases and IX devices were explored in GaAs heterostructures where an IX range of existence is limited to low temperatures due to low IX binding energies. IXs in van der Waals transition-metal dichalcogenide (TMD) heterostructures are characterized by large binding energies giving the opportunity for exploring excitonic quantum gases and for creating excitonic devices at high temperatures. TMD heterostructures also offer a new platform for studying single-exciton phenomena and few-particle complexes. In this work, we present studies of IXs in MoSe$_2$/WSe$_2$ heterostructures and report on two IX luminescence lines whose energy splitting and temperature dependence identify them as neutral and charged IXs. The experimentally found binding energy of the indirect charged excitons, i.e. indirect trions, is close to the calculated binding energy of 28 meV for negative indirect trions in TMD heterostructures [Deilmann, Thygesen, Nano Lett. 18, 1460 (2018)]. We also report on the realization of IXs with a luminescence linewidth reaching 4~meV at low temperatures. An enhancement of IX luminescence intensity and the narrow linewidth are observed in localized spots.

cond-mat.mes-hall↗

arXiv2019

Interference dislocations in condensate of indirect excitons

Phase singularities in quantum states play a significant role both in the state properties and in the transition between the states. For instance, a transition to two-dimensional superfluid state is governed by pairing of vortices and, in turn, unpaired vortices can cause dissipations for particle fluxes. Vortices and other phase defects can be revealed by characteristic features in interference patterns produced by the quantum system. We present dislocation-like phase singularities in interference patterns in a condensate of indirect excitons measured by shift-interferometry. We show that the observed dislocations in interference patterns are not associated with conventional phase defects: neither with vortices, nor with polarization vortices, nor with half-vortices, nor with skyrmions, nor with half-skyrmions. We present the origin of these new phase singularities in condensate interference patterns: the observed interference dislocations originate from converging of the condensate matter waves propagating from different sources.

cond-mat.mes-hall↗

arXiv2019

Exciton gas transport through nano-constrictions

An indirect exciton is a bound state of an electron and a hole in spatially separated layers. Two-dimensional indirect excitons can be created optically in heterostructures containing double quantum wells or atomically thin semiconductors. We study theoretically transmission of such bosonic quasiparticles through nano-constrictions. We show that quantum transport phenomena, e.g., conductance quantization, single-slit diffraction, two-slit interference, and the Talbot effect, are experimentally realizable in systems of indirect excitons. We discuss similarities and differences between these phenomena and their counterparts in electronic devices.

cond-mat.mes-hall↗

arXiv2018

High-mobility indirect excitons in wide single quantum well

Indirect excitons (IXs) are bound pairs of electrons and holes confined in spatially separated layers. We present wide single quantum well (WSQW) heterostructures with high IX mobility, spectrally narrow IX emission, voltage-controllable IX energy, and long and voltage-controllable IX lifetime. This set of properties shows that WSQW heterostructures provide an advanced platform both for studying basic properties of IXs in low-disorder environments and for the development of high mobility excitonic devices.

cond-mat.mes-hall↗

arXiv2018

Split-gate device for indirect excitons

We present a concept and experimental proof of principle for split-gate devices for indirect excitons (IXs). The split-gate forms a narrow channel, a point contact, for IX current. Control of IX flow through the split-gate with both gate voltage and excitation power is demonstrated.

cond-mat.mes-hall↗

arXiv2017

Indirect excitons in van der Waals heterostructures at room temperature

Indirect excitons (IXs) in van der Waals transition-metal dichalcogenide (TMD) heterostructures are characterized by a high binding energy making them stable at room temperature and giving the opportunity for exploring fundamental phenomena in excitonic systems and developing excitonic devices operational at high temperatures. We present the observation of IXs at room temperature in van der Waals TMD heterostructures based on monolayers of MoS$_2$ separated by atomically thin hexagonal boron nitride. The IXs realized in the TMD heterostructure have lifetimes orders of magnitude longer than lifetimes of direct excitons in single-layer TMD, and their energy is gate controlled.

cond-mat.mes-hall↗