arXiv subjects

Kingshuk Mukhuti

Publications and source records attributed to Kingshuk Mukhuti.

7 recordsLinked to original sources

arXiv2026

Observation of an emergent energy scale close to dimensional reduction in a quasi-two-dimensional quantum magnet

By appropriately perturbing a critical transverse-field Ising chain away from its critical point, the system can develop a finite correlation length with a characteristic purely massive spectrum, whose ratios and correlations are precisely described by an integrable field theory and an infinite set of integrals of motion corresponding to the $E_8$ Lie algebra. In this work, we report on experimental observation of a characteristic massive spectrum close to transverse field-induced dimensional reduction in a quasi-two-dimensional quantum magnet Cu$_2$(OH)$_3$Br, providing evidence for an emergent $E_8$ symmetry and the corresponding excitations of bound states in the sublattice of its ferromagnetic chains. These results demonstrate the power of integrable field theory in describing emergent many-body quantum critical phenomena in condensed matter systems.

cond-mat.str-el↗

arXiv2026

Development of a high-field pulsed magnet and optical fiber coupled cryostat system for magneto-photoluminescence measurements

This paper presents the development of a high field pulsed magnet system combined with an optical fiber-coupled low temperature cryostat for magneto-photoluminescence measurements. A novel aspect of our system is the use of electrolyte capacitors in a 75 kJ capacitor bank to drive the pulsed magnet, enabling the generation of high magnetic fields at a relatively low charging voltage (400 V). The zylon reinforced wire wound magnet coil achieves a maximum field strength of 35 tesla with a magnetic field rise time of 10 ms. The integrated cryostat was developed to meet the specific requirements of magneto-photoluminescence experiments using a 4 K helium closed-cycle cryocooler to provide a stable low-temperature environment down to 5 K.

physics.ins-det↗

arXiv2026

Engineering photomagnetism in collinear van der Waals antiferromagnets

Achieving efficient ultrafast optical control of antiferromagnetic spin dynamics is a central goal for next-generation high-speed THz spintronic and magnonic devices. Resonant optical pumping of crystal-field-split d-d orbital multiplets in magnetic TM ions directly modulates exchange and spin-orbit interactions, inducing large-amplitude coherent spin precession. However, such effects are limited to a handful of systems and there is no general strategy to enhance d-d photomagnetism in antiferromagnets. Here, we demonstrate the engineering of photomagnetism via TM-ion doping in collinear van der Waals antiferromagnets. In Mn$_{1-x}$Ni$_x$PS$_3$, small amounts of Ni$^{2+}$ activate a strong photomagnetic response while largely preserving the Néel ground state. Even 10% Ni boosts the response by more than an order of magnitude compared to pure MnPS$_3$, with resonant pumping of Ni$^{2+}$ d-d transitions driving large-amplitude coherent spin precession and providing helicity-dependent phase control. Tuning the pump energy across the full Mn$_{1-x}$Ni$_x$PS$_3$ composition range shows that Ni excitations remain effective across competing Néel and zig-zag antiferromagnetic states while supporting tunable-frequency coherent spin precession. These results establish TM-ion doping as a versatile strategy to harness orbital multiplet excitations for ultrafast, low-dissipation spin control in van der Waals antiferromagnets.

cond-mat.mtrl-sci↗

arXiv2025

Evidence of Athermal Metastable Phase in a Halide Perovskite: Optically Tracked Thermal-Breach Memory

Halide perovskite materials have been extensively studied in the last decade because of their impressive optoelectronic properties. However, their one characteristic that is uncommon for semiconductors is that many undergo thermally induced structural phase transitions. The transition is hysteretic, with the hysteresis window marking the boundary of the metastable phase. We have discovered that in methylammonium lead iodide, this hysteretic metastable phase is athermal, meaning it shows almost no temporal phase evolution under isothermal conditions. We also show that a large number of distinguishable metastable states can be prepared following different thermal pathways. Furthermore, under a reversible thermal perturbation, the states in the metastable phase either show return-point memory or undergo a systematic nonrecoverable phase evolution, depending on the thermal history and the sign of the temperature perturbation. Since the phase fraction can be probed with extreme sensitivity via luminescence, we have an optically retrievable memory that reliably records any breach in temperature stability. Such thermal-breach memory in athermal martensites, of which there are numerous examples, may be useful for tagging packages requiring strict temperature control during transportation or preservation.

cond-mat.mtrl-sci↗

arXiv2022

Carrier thermalization and zero-point bandgap renormalization in halide perovskites from the Urbach tails of the emission spectrum

We develop techniques to study the temperature dependent localization, thermalization, and the effects of phonon scattering on the excitons in halide perovskites from the analysis of the emission spectra. The excitonic Urbach edge, when inferred from the low energy tails of the temperature dependent luminescence spectra, is shown to be sensitive to the electron distribution and thermalization. A method to observe the Urbach focus is devised for halide perovskites where the temperature dependence of the excitonic gap is anomalous. The value of the zero-point bandgap renormalization is inferred to be about 33 meV. This small value of the bandgap renormalization rules out the formation of small polarons and points to weak electron-phonon coupling. The experiments are performed on the nanosheets of the archetypal halide perovskite, CsPbBr$_3$.

cond-mat.mtrl-sci↗

arXiv2020

Dissipation-induced symmetry breaking: Emphanitic transitions in lead- and tin-containing chalcogenides and halide perovskites

Lead and tin-based chalcogenide semiconductors like PbTe or SnSe have long been known to exhibit an unusually low thermal conductivity that makes them very attractive thermoelectric materials. An apparently unrelated fact is that the excitonic bandgap in these materials increases with temperature, whereas for most semiconductors one observes the opposite trend. These two anomalous features are also seen in a very different class of photovoltaic materials, namely the halide-perovskites such as CsPbBr3. It has been previously proposed that emphanisis, a local symmetry-breaking phenomenon, is the one common origin of these unusual features. Discovered a decade ago, emphanisis is the name given to the observed displacement of the lead or the tin ions from their cubic symmetry ground state to a locally distorted phase at high temperature. This phenomenon has been puzzling because it is unusual for the high-temperature state to be of a lower symmetry than the degenerate ground state. Motivated by the celebrated vibration-inversion resonance of the ammonia molecule, we propose a quantum tunneling-based model for emphanisis where decoherence is responsible for the local symmetry breaking with increasing temperature. From the analytic expression of the temperature dependence of the tunnel splitting (which serves as an order parameter), we provide three-parameter fitting formulae which capture the observed temperature dependence of the ionic displacements as well as the anomalous increase of the excitonic bandgap in all the relevant materials.

cond-mat.mtrl-sci↗

arXiv2019

Experimental determination of the bare energy gap of GaAs without the zero-point renormalization

The energy gap of simple band insulators like GaAs is a strong function of temperature due to the electron-phonon interactions. Interestingly, the perturbation from zero-point phonons is also predicted to cause significant (a few percent) renormalization of the energy gap at absolute zero temperature but its value has been difficult to estimate both theoretically and, of course, experimentally. Given the experimental evidence [Bhattacharya, et al., Phys. Rev. Lett. 114, 047402 (2015)] that strongly supports that the exponential broadening (Urbach tail) of the excitonic absorption edge at low temperatures is the manifestation of this zero temperature electron-phonon scattering, we argue that the location of the Urbach focus is the zero temperature unrenormalized gap. Experiments on GaAs yield the zero temperature bare energy gap to be 1.581 eV and thus the renormalization is estimated to be 66 meV.

cond-mat.mtrl-sci↗