arXiv subjects

Mark S. Sherwin

Publications and source records attributed to Mark S. Sherwin.

At least 19 recordsLinked to original sources

arXiv2026

Effective-Hamiltonian reconstruction through Bloch-wave interferometry in bulk GaAs driven by strong THz fields

Reconstructing effective Hamiltonians of condensed matter systems directly from experimental data is challenging because of the intricate relationship between Hamiltonian parameters and observables. Here, we reconstruct an effective three-band electron-hole (e-h) Hamiltonian in bulk GaAs based on high-order sideband generation (HSG) induced by quasi-continuous NIR and THz lasers. We perform polarimetry of high-order sidebands while varying the wavelength and polarization of the NIR laser, as well as the strength of the THz field. An analytic model is derived to incorporate the effects of both dephasing and quantum fluctuations around the semiclassical e-h recollision pathways. Surprisingly, the contribution of quantum fluctuations to the decay of sideband intensity with increasing sideband order is comparable to the contribution of dephasing. We simultaneously and unambiguously determine through Bloch-wave interferometry the effective Hamiltonian parameter that determines the e-h reduced masses, the bandgap of GaAs, and two dephasing constants associated with two e-h species. We demonstrate that full Hamiltonian reconstruction can be achieved by combining HSG measurements with absorbance spectroscopy. Unexpectedly, we find that the extracted bandgap of GaAs is about 10 meV larger than the value inferred from previous absorbance measurements. Quantum-kinetic analysis suggests that, in the HSG experiments, the e-h energy may be renormalized through Fröhlich interaction that is modulated by the strong THz fields. We also show that the energy threshold for optical-phonon emission can be suppressed by applying a strong THz field, leading to nearly constant dephasing rates.

cond-mat.mtrl-sci↗

arXiv2025

Two-fluid mobility model from coupled hydrodynamic equations for simulating laser-driven semiconductor switches

We introduce a two-fluid mobility model incorporating fundamental aspects of electron-hole (e-h) scattering such as momentum conservation for simulating laser-driven semiconductor switches (LDSSs). Compared to previous works that use Matthiessen's rule, the two-fluid mobility model predicts distinct AC responses of e-h plasmas in semiconductors. Based on the two-fluid mobility model, we develop a theory with very few adjustable parameters for simulating the switching performance of LDSSs based on high-purity indirect-gap semiconductors such as silicon (Si). As a prototypical application, we successfully reproduce experimentally measured reflectance at around 320 GHz in a laser-driven Si switch. By injecting e-h plasmas with densities up to $10^{20}\,\rm cm^{-3}$, we reveal the importance of carrier-screening effects in e-h scattering and Auger recombination for carrier densities above the critical carrier density for exciton-plasma Mott transition. Our results also suggest a way to characterize the intrinsic momentum-relaxation mechanism, e-h scattering, and the intrinsic e-h recombination mechanism in indirect-gap semiconductors, Auger recombination. We reassess the ambipolar Auger coefficient of high-purity Si with high injection levels of e-h plasmas up to $10^{20}\,\rm cm^{-3}$ and find a minimal value of $1.8\times10^{-41}\,{\rm cm^6/ns}$. The value is more than one order of magnitude smaller than the ambipolar Auger coefficient widely used for simulating LDSSs, $3.8\times10^{-40}\,{\rm cm^6/ns}$, which was deduced from minority-carrier lifetime in highly doped silicon more than four decades ago.

cond-mat.mtrl-sci↗

arXiv2023

Breaking a Bloch-wave interferometer: quasiparticle species-specific temperature-dependent nonequilibrium dephasing

Recently, high-order sideband polarimetry has been established as an experimental method that links the polarization of sidebands to an interference of Bloch wavefunctions. However, the robustness of sideband polarizations to increasing dephasing remains to be explored. Here, we investigate the dependence of high-order sideband generation in bulk gallium arsenide on dephasing by tuning temperature. We find that the intensities of the sidebands, but not their polarizations, depend strongly on temperature. Using our polarimetry method, we are able to isolate the contributions of electron-heavy hole (HH) and electron-light hole (LH) pairs to sideband intensities, and separately extract the nonequilibrium dephasing coefficients associated with the longitudinal optical (LO) phonons and acoustic (A) phonons for each species of electron-hole pair. We find that $Γ_{\text{HH},\text{A}} = 6.1 \pm 1.6$ $μ$eV/K, $Γ_{\text{LH},\text{A}} < 1.5$ $μ$eV/K, $Γ_{\text{HH},\text{LO}} = 14 \pm 3$ meV, and $Γ_{\text{LH},\text{LO}} = 30 \pm 3$ meV.

cond-mat.mes-hall↗

arXiv2023

Bloch-Wave Interferometry of Driven Quasiparticles in Bulk GaAs

We report that the polarizations of sidebands emitted from bulk gallium arsenide (GaAs) driven by a strong terahertz (THz) laser while probed with a weak near-infrared laser can be viewed as interferograms from a Michelson-like interferometer for Bloch waves. A simple analytical model is introduced to calculate the difference in quantum mechanical phases accumulated by Bloch waves associated with electron-heavy hole and electron-light hole pairs in their respective interferometer arms. The measured and calculated spectra are in good quantitative agreement, including scaling with THz field strength. Our results indicate a simple way to extract material parameters in future experiments

cond-mat.mtrl-sci↗

arXiv2023

Order-of-Magnitude SNR Improvement for High-Field EPR Spectrometers via 3D-Printed Quasioptical Sample Holders

In this paper, we present a rapidly-prototyped, costefficient, 3D-printed quasioptical sample holder for improving the signal-to-noise ratio (SNR) in modern, resonator-free, highfield electron paramagnetic resonance (EPR) spectrometers. Such spectrometers typically operate in induction mode: the detected EPR (cross-polar) signal is polarized orthogonal to the incident (co-polar) radiation. The sample holder improves SNR in three modes: continuous wave, pulsed, and rapid-scan. An adjustable sample positioner allows for optimizing sample position to maximize the 240 GHz magnetic field B1, and a rooftop mirror allows for small rotations of the cross-polar signal to maximize the signal and minimize the co-polar background. When optimized, the co-polar isolation (the ratio of incident to detected co-polar signal) was around 50 dB, an improvement of over 20 dB. This large isolation is especially beneficial for maximizing the SNR of rapidscan EPR, but also improves the SNR in pulsed and cwEPR experiments. Through minimal modification, the sample holder may be incorporated into a variety of homebuilt, induction-mode hfEPR spectrometers in order to significantly improve the SNR (approx. 6x), and thereby reduce the acquisition time (by more than a factor of 30).

physics.ins-det↗

arXiv2023

An explicit formula for high-order sideband polarization by extreme tailoring of Feynman path integrals

High-order sideband generation (HSG), as an analogue of the interband processes in high-harmonic generation (HHG) in solids, is a nonperturbative nonlinear optical phenomenon in semiconductors that are simultaneously driven by a relatively weak near-infrared (NIR) laser and a sufficiently strong terahertz (THz) field. We derive an explicit formula for sideband polarization vectors in a prototypical two-band model based on the saddle-point method. Our formula connects the sideband amplitudes with the laser-field parameters, electronic structures, and nonequilibrium dephasing rates in a highly nontrivial manner. Our results indicate the possibility of extracting information on band structures and dephasing rates from high-order sideband generation experiments with simple algebraic calculations. We also expect our approach to be useful on the quantitative understanding of the interband HHG.

physics.optics↗

arXiv2023

Indium-Bond-And-Stop-Etch (IBASE) Technique for Dual-side Processing of Thin High-mobility GaAs/AlGaAs Epitaxial Layers

We present a reliable flip-chip technique for dual-side processing of thin (<1 micron) high-mobility GaAs/AlGaAs epitaxial layers. The technique allows the fabrication of small (micron-scale with standard UV photolithography) patterned back gates and dual-gate structures on the thin GaAs/AlGaAs films with good alignment accuracy using only frontside alignment. The technique preserves the high-mobility (>10^6 cm^2 /V-s at 2 K) and most (>95%) of the charge density of the 2-dimensional electron gas (2DEG) systems, and allows linear control of the charge density with small (< 1 V) electrostatic gate bias. Our technique is motivated by a novel THz quantum-well detector based on intersubband transitions in a single, wide GaAs/AlGaAs quantum well, in which a symmetric, well-aligned dual-gate structure (with a typical gate dimension of ~5 micron by 5 micron) is required for accurate and precise tuning of the THz detection frequency. Using our Indium-Bond-And-Stop-Etch (IBASE) technique, we realize such dual-gate structure on 660-nm thick GaAs/AlGaAs epitaxial layers that contain a modulation-doped, 40-nm wide, single square quantum well. By independently controlling the charge density and the DC electric field set between the gates, we demonstrate robust tuning of the intersubband absorption behavior of the 40-nm quantum well near 3.44 THz at 30 K.

physics.ins-det↗

arXiv2019

Dressed Rabi oscillation in a crystalline organic radical

Free electron laser-powered pulsed electron paramagnetic resonance (EPR) experiments performed at 240 GHz / 8.56 T on the crystalline organic radical BDPA reveal a tip-angle dependent resonant frequency. Frequency shifts as large as 11 MHz (45 ppm) are observed during a single Rabi oscillation. We attribute the frequency shifts to a "dressing" of the nutation by spin-spin interactions. A nonlinear semi-classical model which includes a temperature- and sample-geometry-dependent demagnetizing field reproduces experimental results. Because experiments are performed without a cavity, radiation damping -- the most common nonlinear interaction in magnetic resonance -- is negligible in our experiments.

cond-mat.mes-hall↗

arXiv2017

Dynamical birefringence: Electron-hole recollisions as probes of Berry curvature

The direct measurement of Berry phases is still a great challenge in condensed matter systems. The bottleneck has been the ability to adiabatically drive an electron coherently across a large portion of the Brillouin zone in a solid where the scattering is strong and complicated. We break through this bottleneck and show that high-order sideband generation (HSG) in semiconductors is intimately affected by Berry phases. Electron-hole recollisions and HSG occur when a near-band gap laser beam excites a semiconductor that is driven by sufficiently strong terahertz (THz)-frequency electric fields. We carried out experimental and theoretical studies of HSG from three GaAs/AlGaAs quantum wells. The observed HSG spectra contain sidebands up to the 90th order, to our knowledge the highest-order optical nonlinearity observed in solids. The highest-order sidebands are associated with electron-hole pairs driven coherently across roughly 10% of the Brillouin zone around the Γpoint. The principal experimental claim is a dynamical birefringence: the sidebands, when the order is high enough (> 20), are usually stronger when the exciting near-infrared (NIR) and the THz electric fields are polarized perpendicular than parallel; the sideband intensities depend on the angles between the THz field and the crystal axes in samples with sufficiently weak quenched disorder; and the sidebands exhibit significant ellipticity that increases with increasing sideband order, despite nearly linear excitation and driving fields. We explain dynamical birefringence by generalizing the three-step model for high order harmonic generation. The hole accumulates Berry phases due to variation of its internal state as the quasi-momentum changes under the THz field. Dynamical birefringence arises from quantum interference between time-reversed pairs of electron-hole recollision pathways.

cond-mat.mtrl-sci↗

arXiv2016

Gd$^{3+}$ - Gd$^{3+}$ distances exceeding 3 nm determined by very high frequency continuous wave electron paramagnetic resonance

Electron paramagnetic resonance spectroscopy in combination with site-directed spin-labeling is a very powerful tool for elucidating the structure and organization of biomolecules. Gd$^{3+}$ complexes have recently emerged as a new class of spin labels for distance determination by pulsed EPR spectroscopy at Q- and W-band. We present CW EPR measurements at 240 GHz (8.6 Tesla) on a series of Gd-rulers of the type Gd-PyMTA---spacer---Gd-PyMTA, with Gd-Gd distances ranging from 1.2 nm to 4.3 nm. CW EPR measurements of these Gd-rulers show that significant dipolar broadening of the central $|-1/2\rangle\rightarrow|1/2\rangle$ transition occurs at 30 K for Gd-Gd distances up to $\sim$ 3.4 nm with Gd-PyMTA as the spin label. This represents a significant extension for distances accessible by CW EPR, as nitroxide-based spin labels at X-band frequencies can typically only access distances up to $\sim$ 2 nm. We show that this broadening persists at biologically relevant temperatures above 200 K, and that this method is further extendable up to room temperature by immobilizing the sample in glassy trehalose. We show that the peak-to-peak broadening of the central transition follows the expected $~1/r^3$ dependence for the electron-electron dipolar interaction, from cryogenic temperatures up to room temperature. A simple procedure for simulating the dependence of the lineshape on interspin distance is presented, in which the broadening of the central transition is modeled as an $S=1/2$ spin whose CW EPR lineshape is broadened through electron-electron dipolar interactions with a neighboring $S=7/2$ spin.

physics.bio-ph↗

arXiv2015

High-precision gigahertz-to-terahertz spectroscopy of aqueous salt solutions as a probe of the femtosecond-to-picosecond dynamics of liquid water

Because it is sensitive to fluctuations occurring over femtoseconds to picoseconds, gigahertz-to-terahertz dielectric relaxation spectroscopy can provide a valuable window into water's most rapid intermolecular motions. In response, we have built a vector network analyzer dielectric spectrometer capable of measuring absorbance and index of refraction in this frequency regime with unprecedented precision. Using this to determine the complex dielectric response of water and aqueous salt solutions from 5.9 GHz to 1.12 THz (which we provide in the SI), we have obtained strong new constraints on theories of water's collective dynamics. For example, while the salt-dependencies we observe for water's two slower relaxations (8 and 1 ps) are easily reconciled with suggestions that they arise due to rotations of fully and partially hydrogen bonded molecules, respectively, the salt-dependence of the fastest relaxation (180 fs) appears difficult to reconcile with its prior assignment to liberations of single hydrogen bonds.

physics.chem-ph↗

arXiv2015

Theory of low power ultra-broadband terahertz sideband generation in bi-layer graphene

In a semiconductor illuminated by a strong terahertz field, optically excited electron-hole pairs can recombine to emit light in a broad frequency comb evenly spaced by twice the terahertz frequency. Such high-order terahertz sideband generation is of interest both as an example of extreme nonlinear optics and also as a method for ultrafast electro-optical modulation. So far, this phenomenon has only been observed with large field strengths (~10 kVcm-1), an obstacle for technological applications. Here we predict that bi-layer graphene generates high-order sidebands at much weaker terahertz fields. We find that a terahertz field of strength 1 kVcm-1 can produce a high-sideband spectrum of about 30 THz, 100 times broader than in GaAs. The sidebands are generated despite the absence of classical collisions, with the quantum coherence of the electron-hole pairs enabling recombination. These remarkable features lower the barrier to desktop electro-optical modulation at terahertz frequencies, facilitating ultrafast optical communications.

cond-mat.mes-hall↗

arXiv2014

Terahertz electron-hole recollisions in GaAs/AlGaAs quantum wells: robustness to scattering by optical phonons and thermal fluctuations

Electron-hole recollisions are induced by resonantly injecting excitons with a near-IR laser at frequency $f_{\text{NIR}}$ into quantum wells driven by a ~10 kV/cm field oscillating at $f_{\text{THz}} = 0.57$ THz. At $T=12$ K, up to 18 sidebands are observed at frequencies $f_{\text{sideband}}=f_{\text{NIR}}+2n f_{\text{THz}}$, with $-8 \le 2n \le 28$. Electrons and holes recollide with total kinetic energies up to 57 meV, well above the $E_{\text{LO}} = 36$ meV threshold for longitudinal optical (LO) phonon emission. Sidebands with order up to $2n=22$ persist up to room temperature. A simple model shows that LO phonon scattering suppresses but does not eliminate sidebands associated with kinetic energies above $E_{\text{LO}}$.

cond-mat.mes-hall↗

arXiv2013

Self-assembled ErSb nanostructures of tunable shape and orientation: growth and plasmonic properties

Self-assembled, semimetallic ErSb single crystal nanostructures, grown by molecular beam epitaxy, are embedded within a semiconductor GaSb matrix. Formation, evolution and orientation of a variety of nanostructures, including spherical nanoparticles, elongated nanorods, octagonal shaped nanowires oriented along the surface normal and nanowires oriented in the growth plane, are controlled simply by the Er fraction. The plasmonic properties of the semimetal/semiconductor composites are characterized and quantified by three polarization-resolved spectroscopy techniques, spanning more than three orders of magnitude in frequency from 100 GHz up to 300 THz. The effect of the size, shape and orientation of the nanostructures is characterized by polarization-sensitive response and modeled by a Maxwell-Garnett effective medium theory.

cond-mat.mtrl-sci↗

arXiv2012

High-order sideband generation in bulk GaAs

When an intense THz field at frequency f_THz is applied to excitons resonantly created in bulk GaAs by a near IR laser at frequency f_NIR, sidebands are observed at frequencies f_sideband = f_NIR + 2nf_THz, where n is an integer. At temperature T=10 K, sidebands of order -4 {greater than or equal to} 2n {greater than or equal to} 16 are observed. Sidebands up to 10th order persist at 170 K.

cond-mat.mes-hall↗

arXiv2011

THz driven quantum wells: Coulomb interactions and Stark shifts in the ultrastrong coupling regime

We investigate the near infrared interband absorption of semiconductor quantum wells driven by intense terahertz radiation in the regime of ultrastrong coupling, where the Rabi frequency is a significant fraction of the frequency of the strongly driven transition. With the driving frequency tuned just below the lowest frequency transition between valence subbands, a particularly interesting phenomenon is observed. As the THz power increases, a new peak emerges above the frequency of the undriven exciton peak which grows and eventually becomes the larger of the two. This reversal of relative peak intensity is inconsistent with the Autler-Townes effect in a three-state system while within the rotating wave approximation (RWA). In the samples investigated, the Bloch-Siegert shift (associated with abandoning the RWA), exciton binding energy, the Rabi energy, and non-resonant AC Stark effects are all of comparable magnitude. Solution of a semiconductor Bloch model with one conduction and multiple valence subbands indicates that the AC Stark effect is predominantly responsible for the observed phenomenon.

cond-mat.mes-hall↗

arXiv2009

Cavity dumping of an injection-locked free-electron laser

This letter reports cavity dumping of an electrostatic-accelerator-driven free-electron laser (FEL) while it is injection-locked to a frequency-stabilized 240 GHz solid-state source. Cavity dumping enhances the FEL output power by a factor of $\sim$8, and abruptly cuts off the end of the FEL pulse. The cavity-dumped, injection-locked FEL output is used in a 240 GHz pulsed electron spin resonance (ESR) experiment.

cond-mat.other↗

arXiv2008

Coherent Manipulation and Decoherence of S=10 Single-Molecule Magnets

We report coherent manipulation of S=10 Fe$_{8}$ single-molecule magnets. The temperature dependence of the spin decoherence time $T_2$ measured by high frequency pulsed electron paramagnetic resonance indicates that strong spin decoherence is dominated by Fe$_{8}$ spin bath fluctuations. By polarizing the spin bath in Fe$_{8}$ single-molecule magnets at magnetic field $B$ = 4.6 T and temperature $T$ = 1.3 K, spin decoherence is significantly suppressed and extends the spin decoherence time $T_2$ to as long as 712 ns. A second decoherence source is likely due to fluctuations of the nuclear spin bath. This hints that the spin decoherence time can be further extended via isotopic substitution to smaller magnetic moments.

cond-mat.mes-hall↗