arXiv subjects

Atac Imamoglu

Publications and source records attributed to Atac Imamoglu.

At least 19 recordsLinked to original sources

arXiv2026

Nonequilibrium dynamics of doped Chern ferromagnets: a case study for false vacuum decay

Even though metastable false vacuum decay is ubiquitous in physics, its underlying dynamics are still not well understood. Dissipative state preparation in moir\'e quantum materials provides an exceptional setting for exploring this physics since it allows the possibility of generating exotic quantum states that are not the ground state of the system Hamiltonian. Motivated by recent experiments demonstrating steady-state optical orientation of the spin-valley degree of freedom of holes, here we investigate dynamics of itinerant and Chern ferromagnets in the presence of an opposing magnetic field. Optical pumping using a circularly polarized Laguerre-Gauss beam allows us to deterministically prepare a true vacuum bubble embedded inside a metastable state. Depending on its initial size controlled by the pump power, we observe that the bubble collapses or expands due to an interplay between domain wall and bulk dynamics. For external magnetic fields comparable to the coercive field of ferromagnetism, we observe up to two-orders-of-magnitude prolongation of the spin polarization decay time at commensurate fillings corresponding to integer and fractional Chern insulator states. Our experiments reveal that the nonequilibrium dynamics of the ferromagnetic domains is substantially more sensitive to the precise filling factor around Chern insulator states than standard transport or optical measurements.

cond-mat.str-el↗

arXiv2026

Cavity control of quantum phase transitions in a two-dimensional Kondo lattice

Cavity quantum electrodynamics offers a route to control quantum phases by using vacuum fluctuations of confined electromagnetic fields. In particular, planar cavities based on polar van der Waals materials can generate strongly confined modes and are promising for controlling two-dimensional correlated materials. Recently, moir\'e materials have become central platforms for studying two-dimensional heavy-fermion systems and their quantum phase transitions. Kondo lattices provide a prototypical model for studying quantum phase boundaries, driven by competition between Kondo screening and the ordering of local magnetic moments. We show that a cavity-induced interaction can shift the quantum phase transitions between a heavy-fermion phase and an antiferromagnetic phase in a two-dimensional Kondo lattice through a momentum-dependent self-energy of the conduction bands. For the longitudinal projected field motivated by h-BN hyperbolic phonon polaritons, the self-energy favors Kondo hybridization and expands the heavy-fermion region. Transverse and circular in-plane model structures give distinct effects, with the transverse case relatively favoring the magnetically ordered phase and the circular case lying between the longitudinal and transverse cases. These results indicate that electromagnetic vacuum fluctuations can effectively modify the control parameters of strongly correlated two-dimensional Kondo materials.

cond-mat.str-el↗

arXiv2026

Photon Correlation Spectroscopy as a Probe of Critical Fluctuations in Correlated Electron Systems

Characterizing phase transitions between correlated electronic phases, extracting their critical exponents, and identifying their universality class are of central interest in many-body physics. Here, we propose and demonstrate that photon correlation spectroscopy can be used to gain insight into the nature of critical electronic density fluctuations. We study a semiconductor moir\'e material consisting of two MoSe2 layers separated by a monolayer h-BN spacer and measure interlayer electron dynamics via the second-order correlation function of the scattered photons. The correlated transfer of large numbers of electrons between the layers at the onset of an Ising-type layer pseudo-spin phase transition leads to photon bunching in light scattered by the exciton resonance of one layer. Our measurements pave the way for using photon correlations as a method to access dynamical exponents associated with electronic phase transitions.

cond-mat.str-el↗

arXiv2026

Driven-dissipative superconductivity in moir\'e heterostructure without attraction

Dissipative preparation of quantum order offers a route to superconductivity that does not rely on enhancing attractive interactions. Here we propose a driven-dissipative protocol to prepare superconductivity as a stationary state of a two-dimensional moir\'e heterostructure. The key ingredient is a bilayer moir\'e platform in which the layer degree of freedom acts as a pseudospin, allowing the pseudospin structure required for pairing to be implemented through optically induced spatial operations. This preparation scheme requires local dissipation, which we show to arises naturally from weakly dispersive bosonic modes in the heterostructure. In contrast, in the opposite regime of collective dissipation, the same platform exhibits an early-time superradiant burst. Our results establish driven-dissipative moir\'e heterostructures as a promising platform for preparing superconductivity, while also revealing a connection between steady-state pairing and transient superradiance.

cond-mat.str-el↗

arXiv2026

Quantum correlations and dissipative blockade of polaritons in a tunable fiber cavity

Cavity exciton--polaritons are quasiparticles that form when quantum well excitons hybridize with a cavity mode. Here, we carry out photon correlation measurements under continuous wave resonant laser excitation to demonstrate quantum correlations between cavity--polaritons. Our experiments reveal an unexpectedly strong dependence of polariton interactions on cavity--exciton detuning. When the polaritons are predominantly exciton-like, we observe a transition from photon antibunching to bunching as the laser is tuned across the polariton resonance, in agreement with a simple Kerr-nonlinearity model. When the lower-branch polariton energy is tuned to induce a two-polariton Feshbach resonance with the biexciton mode, the degree of polariton antibunching becomes independent of the laser detuning: we explain our finding by invoking a dissipative blockade mechanism arising from large biexciton broadening. Our experiments demonstrate that the strong polariton blockade regime would be achieved by reducing the polariton decay rate by a factor of 10.

cond-mat.mes-hall↗

arXiv2025

Wigner polarons reveal Wigner crystal dynamics in a monolayer semiconductor

Wigner crystals, lattices made purely of electrons, are a quintessential paradigm of studying correlation-driven quantum phase transitions. Despite decades of research, the internal dynamics of Wigner crystals has remained extremely challenging to access, with most experiments probing only static order or collective motion. Here, we establish monolayer WSe2 as a new materials platform to host zero-field Wigner crystals and then demonstrate that exciton spectroscopy provides a direct means to probe both static and dynamic properties of these electron lattices. We uncover striking optical resonances that we identify as Wigner polarons, quasiparticles formed when the electron lattice is locally distorted by exciton-Wigner crystal coupling. We further achieve all-optical control of spins in the Wigner crystal, directly probing valley-dependent Wigner polaron scattering well above the magnetic ordering temperature and in the absence of any external magnetic field. Finally, we demonstrate optical melting of the Wigner crystal and observe intriguingly different responses of the umklapp (static) and Wigner polaron (dynamic) resonances to optical excitation. Our results open up exciting new avenues for elucidating electron dynamics and achieving ultrafast optical control of interaction-driven quantum phase transitions in strongly correlated electron systems.

cond-mat.mes-hall↗

arXiv2025

Theory of exciton polarons in 2D Wigner crystals

Monolayer transition-metal dichalcogenides (TMDs) provide a platform for realizing Wigner crystals and enable their detection via exciton spectroscopy. We develop a microscopic theoretical model for excitons interacting with the localized electrons of the Wigner crystal, including their vibrational motion. In addition to the previously observed exciton-Umklapp feature, the theory reproduces and explains the higher-band attractive-polaron resonances recently reported experimentally. Our model further uncovers that the appearance of two equal-strength and parallel attractive polarons, as commonly observed in WSe$_2$ and WS$_2$, is a signature of strong correlations in the electronic system. Altogether, our results demonstrate that accounting for electronic interactions is essential to reproduce and interpret the exciton-polaron spectra of TMDs.

cond-mat.str-el↗

arXiv2025

Long-range ferroelectric order in two dimensional excitonic insulators

It is generally argued that Mermin-Wagner theorem excludes the possibility of long-range order in two dimensional bosonic systems at non-zero temperatures. In contrast, we show here that generic bilayer semiconductors could demonstrate true Bose-Einstein condensation of interlayer excitons. We show that the key requirements include (i) reduction of the interlayer band gap using an applied electric field so that excitons spontaneously appear in the ground state, (ii) band structure that allows for long-range electron-hole exchange interaction, and (iii) a finite magnetic field. Our results indicate that superfluidity and ferroelectric order can co-exist in two dimensional excitonic insulators.

cond-mat.str-el↗

arXiv2025

Optical control over topological Chern number in moir\'e materials

Controlling quantum matter with light offers a promising route to dynamically tune its many-body properties, ranging from band topology to superconductivity. However, achieving such optical control for strongly correlated electron systems in the steady-state has remained elusive. Here, we demonstrate all-optical switching of the spin-valley degree of freedom of itinerant ferromagnets in twisted MoTe2 homobilayers. This system uniquely features flat valley-contrasting Chern bands and exhibits a range of strongly correlated phases at various moir\'e lattice fillings, including Chern insulators and ferromagnetic metals. We show that the spin-valley orientation of all of these phases can be dynamically reversed by resonantly exciting the attractive polaron transition with circularly-polarized light. These findings not only constitute the first direct evidence for non-thermal switching of a ferromagnetic spin state at zero magnetic field, but also demonstrate the possibility of dynamical control over topological order parameter, paving the way for all-optical generation of chiral edge modes and topological quantum circuits.

cond-mat.mes-hall↗

arXiv2025

Asymmetric trions in monolayer transition metal dichalcogenides

Exciton spectroscopy serves as a sensitive probe of electronic states in two-dimensional semiconductors. A prominent feature in optical spectra is the trion peak arising from the binding of a charge carrier to an exciton. The splitting between the exciton and trion peaks is usually interpreted as the trion binding energy, but we theoretically show that this view is incomplete. Since dark excitons are more strongly bound than the bright exciton, the trion wave function is asymmetric and a large contribution to the measured splitting is the difference between the bright and dark exciton binding energies. Our model quantitatively explains the measured trion energies in MoSe2 and WSe2, demonstrating the importance of the internal structure of the exciton for the interpretation of the optical response of transition metal dichalcogenides.

cond-mat.mes-hall↗

arXiv2025

Is Lindblad for me?

The Lindblad master equation is a foundational tool for modeling the dynamics of open quantum systems. As its use has extended far beyond its original domain, the boundaries of its validity have grown opaque. In particular, the rise of new research areas including open quantum many-body systems, non-equilibrium condensed matter, and the possibility to test its limits in driven-open quantum simulators, call for a critical revision of its regimes of applicability. In this pedagogical review, we re-examine the folklore surrounding its three standard approximations (Born, Markov, and Rotating Wave Approximation), as we build our narrative by employing a series of examples and case studies accessible to any reader with a solid background on the fundamentals of quantum mechanics. As a synthesis of our work, we offer a checklist that contrasts common lore with refined expectations, offering a practical guideline for assessing the breakdown of the Lindblad framework in the problem at hand.

quant-ph↗

arXiv2024

Quantum impurities in finite-temperature Bose gases: Detecting vortex proliferation across the BKT and BEC transitions

Detecting vortices in neutral superfluids represents an outstanding experimental challenge. Using stochastic classical-field methods, we theoretically show that a quantum impurity repulsively coupled to a weakly-interacting Bose gas at finite temperature carries direct spectroscopic signatures of vortex proliferation. In two dimensions, we find that a low-energy (attractive) branch in the excitation spectrum becomes prominent when the temperature is tuned across the Berezinskii-Kosterlitz-Thouless (BKT) transition. We explain this red-shifted resonance as originating from the binding of the impurity to vortices, where the bosons density (and hence, the repulsive Hartree energy) is reduced. This mechanism could be exploited to spectroscopically estimate the BKT transition in excitonic insulators. In contrast, in three dimensions, the impurity spectra reflect the presence of vortex rings well below the condensation temperature, and herald the presence of a thermal gas above the Bose-Einstein condensation transition. Importantly, we expect our results to have impact on the understanding of Bose-polaron formation at finite temperatures.

cond-mat.quant-gas↗

arXiv2024

First order Quantum Hall to Wigner crystal phase transition on a triangular lattice: an iDMRG study

In this work we study a system of interacting fermions on a triangular lattice in the presence of an external magnetic field. We neglect spin and fix a density of one third, with one unit of magnetic flux per particle. The infinite density matrix renormalization group algorithm is used to compute the ground state of this generalized Fermi-Hubbard model. Increasing the strength of the nearest-neighbor repulsion, we find a first order transition between an Integer Quantum Hall phase and a crystalline, generalized Wigner crystal state. The first-order nature of the phase transition is consistent with a Ginzburg-Landau argument. We expect our results to be relevant for moir\'e heterostructures of two-dimensional materials.

cond-mat.str-el↗

arXiv2024

Confined Trions and Mott-Wigner States in a Purely Electrostatic Moir\'e Potential

Moir\'e heterostructures consisting of transition metal dichalcogenide (TMD) hetero- and homobilayers have emerged as a promising material platform to study correlated electronic states. Optical signatures of strong correlations in the form of Mott-Wigner states and fractional Chern insulators have already been observed in TMD monolayers and their twisted bilayers. In this work, we use a moir\'e substrate containing a twisted hexagonal boron nitride (h-BN) interface to externally generate a superlattice potential for the TMD layer: the periodic structure of ferroelectric domains in h-BN effects a purely electrostatic potential for charge carriers. We find direct evidence for the induced moir\'e potential in the emergence of new excitonic resonances at integer fillings, and our observation of an enhancement of the trion binding energy by $\simeq$ 3 meV. A theoretical model for exciton-electron interactions allows us to directly determine the moir\'e potential modulation of 30$\pm$5 meV from the measured trion binding energy shift. We obtain direct evidence for charge order linked to electronic Mott-Wigner states at filling factors $\nu$ = 1/3 and $\nu$ = 2/3 through the associated exciton Umklapp resonances.

cond-mat.str-el↗

arXiv2024

Electrically defined quantum dots for bosonic excitons

Quantum dots are semiconductor nano-structures where particle motion is confined in all three spatial dimensions. Since their first experimental realization, nanocrystals confining the quanta of polarization waves, termed excitons, have found numerous applications in fields ranging from single photon sources for quantum information processing to commercial displays. A major limitation to further extending the range of potential applications has been the large inhomogeneity in, and lack-of tunability of, exciton energy that is generic to quantum dot materials. Here, we address this challenge by demonstrating electrically-defined quantum dots for excitons in monolayer semiconductors where the discrete exciton energies can be tuned using applied gate voltages. Resonance fluorescence measurements show strong spectral jumps and blinking of these resonances, verifying their zero-dimensional nature. Our work paves the way for realizing quantum confined bosonic modes where nonlinear response would arise exclusively from exciton--exciton interactions.

cond-mat.mes-hall↗

arXiv2023

Superconductivity induced by strong electron-exciton coupling in doped atomically thin semiconductor heterostructures

We study a mechanism to induce superconductivity in atomically thin semiconductors where excitons mediate an effective attraction between electrons. Our model includes interaction effects beyond the paradigm of phonon-mediated superconductivity and connects to the well-established limits of Bose and Fermi polarons. By accounting for the strong-coupling physics of trions, we find that the effective electron-exciton interaction develops a strong frequency and momentum dependence accompanied by the system undergoing an emerging BCS-BEC crossover from weakly bound $s$-wave Cooper pairs to a superfluid of bipolarons. Even at strong-coupling the bipolarons remain relatively light, resulting in critical temperatures of up to 10\% of the Fermi temperature. This renders heterostructures of two-dimensional materials a promising candidate to realize superconductivity at high critical temperatures set by electron doping and trion binding energies.

cond-mat.mes-hall↗

arXiv2023

Interaction induced AC-Stark shift of exciton-polaron resonances

Laser induced shift of atomic states due to the AC-Stark effect has played a central role in cold-atom physics and facilitated their emergence as analog quantum simulators. Here, we explore this phenomena in an atomically thin layer of semiconductor MoSe$_2$, which we embedded in a heterostructure enabling charge tunability. Shining an intense pump laser with a small detuning from the material resonances, we generate a large population of virtual collective excitations, and achieve a regime where interactions with this background population is the leading contribution to the AC-Stark shift. Using this technique we study how itinerant charges modify -- and dramatically enhance -- the interactions between optical excitations. In particular, our experiments show that the interaction between attractive polarons could be more than an order of magnitude stronger than those between bare excitons.

cond-mat.mes-hall↗

arXiv2023

Kinetic Magnetism in Triangular Moir\'e Materials

Magnetic properties of materials ranging from conventional ferromagnetic metals to strongly correlated materials such as cuprates originate from Coulomb exchange interactions. The existence of alternate mechanisms for magnetism that could naturally facilitate electrical control have been discussed theoretically but an experimental demonstration in an extended system has been missing. Here, we investigate MoSe$_2$/WS$_2$ van der Waals heterostructures in the vicinity of Mott insulator states of electrons forming a frustrated triangular lattice and observe direct evidence for magnetic correlations originating from a kinetic mechanism. By directly measuring electronic magnetization through the strength of the polarization-selective attractive polaron resonance, we find that when the Mott state is electron doped the system exhibits ferromagnetic correlations in agreement with the Nagaoka mechanism.

cond-mat.str-el↗