arXiv subjects

L. H. Fowler-Gerace

Publications and source records attributed to L. H. Fowler-Gerace.

10 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↗

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

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.

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