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Probing Topological Surface States and Conduction via Extended Defects in (Bi$_{1-x}$Sb$_x$)$_2$Te$_3$ Films
Authors:
Abby Liu,
Armando Gil,
Moon-ki Choi,
Berna Akgenc Hanedar,
Zecheng You,
Shriya Sinha,
Tahsin Hakioglu,
Harley T. Johnson,
Kai Sun,
Roy Clarke,
Ctirad Uher,
Cagliyan Kurdak,
Rachel S. Goldman
Abstract:
(Bi$_{1-x}$Sb$_x$)$_2$Te$_3$ alloys are non-degenerate topological insulators (TIs) whose Dirac point (DP) can be tuned within the bulk bandgap by varying the composition, effectively reducing bulk conduction while allowing surface carrier conduction. Magnetotransport measurements of a series of (Bi$_{1-x}$Sb$_x$)$_2$Te$_3$ thin films indicate electron-dominated conduction, with weak anti-localiza…
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(Bi$_{1-x}$Sb$_x$)$_2$Te$_3$ alloys are non-degenerate topological insulators (TIs) whose Dirac point (DP) can be tuned within the bulk bandgap by varying the composition, effectively reducing bulk conduction while allowing surface carrier conduction. Magnetotransport measurements of a series of (Bi$_{1-x}$Sb$_x$)$_2$Te$_3$ thin films indicate electron-dominated conduction, with weak anti-localization attributed to topological surface states (TSSs). Due to the similarity of phase coherence lengths and twin boundary spacings ($\sim$100 nm), we consider the role of twin boundaries as additional conducting paths. Density functional theory calculations reveal an enhanced density of states near the Fermi level at $60^\circ$ twin boundaries, with 2D carrier concentration in excess of $3 \times 10^{13}$ cm$^{-2}$. Furthermore, an analysis of the longitudinal magnetoconductivity yields an upper bound of $7.3 \times 10^{-4}$ S for twin boundary conductivity, resulting in a carrier mobility as high as $142$ cm$^2$/(V$\cdot$s). We discuss the role of twin boundaries in facilitating a transition from a massive Dirac cone dispersion to gapless, topologically protected surface states. Understanding the role of twin boundaries on carrier conduction in non-degenerate TIs is critical for the development of novel TI-based electronic devices.
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Submitted 16 December, 2025; v1 submitted 13 December, 2025;
originally announced December 2025.
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Terahertz-induced tunnel ionization drives coherent Raman-active phonon in Bismuth
Authors:
Bing Cheng,
Patrick L. Kramer,
Mariano Trigo,
Mengkun Liu,
Ctirad Uher,
David A. Reis,
Zhi-Xun Shen,
Jonathan A. Sobota,
Matthias. C. Hoffmann
Abstract:
Driving coherent lattice motion with THz pulses has emerged as a novel pathway for achieving dynamic stabilization of exotic phases that are inaccessible in equilibrium quantum materials. In this work, we present a previously unexplored mechanism for THz excitation of Raman-active phonons. We show that intense THz pulses centered at 1 THz can excite the Raman-active $A_{1g}$ phonon mode at 2.9 THz…
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Driving coherent lattice motion with THz pulses has emerged as a novel pathway for achieving dynamic stabilization of exotic phases that are inaccessible in equilibrium quantum materials. In this work, we present a previously unexplored mechanism for THz excitation of Raman-active phonons. We show that intense THz pulses centered at 1 THz can excite the Raman-active $A_{1g}$ phonon mode at 2.9 THz in a bismuth film. We rule out the possibilities of the phonon being excited through conventional anharmonic coupling to other modes or via a THz sum frequency process. Instead, we demonstrate that the THz-driven tunnel ionization provides a plausible means of creating a displacive driving force to initiate the phonon oscillations. Our work highlights a new mechanism for exciting coherent phonons, offering potential for dynamic control over the electronic and structural properties of semimetals and narrow-band semiconductors on ultrafast timescales.
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Submitted 18 September, 2025; v1 submitted 11 August, 2024;
originally announced August 2024.
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Ultrafast measurements of mode-specific deformation potentials of Bi$_2$Te$_3$ and Bi$_2$Se$_3$
Authors:
Yijing Huang,
José D. Querales-Flores,
Samuel W. Teitelbaum,
Jiang Cao,
Thomas Henighan,
Hanzhe Liu,
Mason Jiang,
Gilberto De la Peña,
Viktor Krapivin,
Johann Haber,
Takahiro Sato,
Matthieu Chollet,
Diling Zhu,
Tetsuo Katayama,
Robert Power,
Meabh Allen,
Costel R. Rotundu,
Trevor P. Bailey,
Ctirad Uher,
Mariano Trigo,
Patrick S. Kirchmann,
Éamonn D. Murray,
Zhi-Xun Shen,
Ivana Savic,
Stephen Fahy
, et al. (2 additional authors not shown)
Abstract:
Quantifying electron-phonon interactions for the surface states of topological materials can provide key insights into surface-state transport, topological superconductivity, and potentially how to manipulate the surface state using a structural degree of freedom. We perform time-resolved x-ray diffraction (XRD) and angle-resolved photoemission (ARPES) measurements on Bi$_2$Te$_3$ and Bi$_2$Se…
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Quantifying electron-phonon interactions for the surface states of topological materials can provide key insights into surface-state transport, topological superconductivity, and potentially how to manipulate the surface state using a structural degree of freedom. We perform time-resolved x-ray diffraction (XRD) and angle-resolved photoemission (ARPES) measurements on Bi$_2$Te$_3$ and Bi$_2$Se$_3$, following the excitation of coherent A$_{1g}$ optical phonons. We extract and compare the deformation potentials coupling the surface electronic states to local A$_{1g}$-like displacements in these two materials using the experimentally determined atomic displacements from XRD and electron band shifts from ARPES.We find the coupling in Bi$_2$Te$_3$ and Bi$_2$Se$_3$ to be similar and in general in agreement with expectations from density functional theory. We establish a methodology that quantifies the mode-specific electron-phonon coupling experimentally, allowing detailed comparison to theory. Our results shed light on fundamental processes in topological insulators involving electron-phonon coupling.
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Submitted 22 July, 2023;
originally announced July 2023.
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Influence of local symmetry on lattice dynamics coupled to topological surface states
Authors:
Jonathan A. Sobota,
Samuel W. Teitelbaum,
Yijing Huang,
José D. Querales-Flores,
Robert Power,
Meabh Allen,
Costel R. Rotundu,
Trevor P. Bailey,
Ctirad Uher,
Tom Henighan,
Mason Jiang,
Diling Zhu,
Matthieu Chollet,
Takahiro Sato,
Mariano Trigo,
Éamonn D. Murray,
Ivana Savić,
Patrick S. Kirchmann,
Stephen Fahy,
David. A. Reis,
Zhi-Xun Shen
Abstract:
We investigate coupled electron-lattice dynamics in the topological insulator Bi2Te3 with time-resolved photoemission and time-resolved x-ray diffraction. It is well established that coherent phonons can be launched by optical excitation, but selection rules generally restrict these modes to zone-center wavevectors and Raman-active branches. We find that the topological surface state couples to ad…
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We investigate coupled electron-lattice dynamics in the topological insulator Bi2Te3 with time-resolved photoemission and time-resolved x-ray diffraction. It is well established that coherent phonons can be launched by optical excitation, but selection rules generally restrict these modes to zone-center wavevectors and Raman-active branches. We find that the topological surface state couples to additional modes, including a continuum of surface-projected bulk modes from both Raman- and infrared-branches, with possible contributions from surface-localized modes when they exist. Our calculations show that this surface vibrational spectrum occurs naturally as a consequence of the translational and inversion symmetries broken at the surface, without requiring the splitting-off of surface-localized phonon modes. The generality of this result suggests that coherent phonon spectra are useful by providing unique fingerprints for identifying surface states in more controversial materials. These effects may also expand the phase space for tailoring surface state wavefunctions via ultrafast optical excitation.
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Submitted 19 December, 2022;
originally announced December 2022.
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All-optical probe of three-dimensional topological insulators based on high-harmonic generation by circularly-polarized laser fields
Authors:
Denitsa Baykusheva,
Alexis Chacón,
Jian Lu,
Trevor P. Bailey,
Jonathan A. Sobota,
Hadas Soifer,
Patrick S. Kirchmann,
Costel R. Rotundu,
Ctirad Uher,
Tony F. Heinz,
David A. Reis,
Shambhu Ghimire
Abstract:
We report the observation of a novel nonlinear optical response from the prototypical three-dimensional topological insulator Bi$_2$Se$_3$ through the process of high-order harmonic generation. We find that the generation efficiency increases as the laser polarization is changed from linear to elliptical, and it becomes maximum for circular polarization. With the aid of a microscopic theory and a…
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We report the observation of a novel nonlinear optical response from the prototypical three-dimensional topological insulator Bi$_2$Se$_3$ through the process of high-order harmonic generation. We find that the generation efficiency increases as the laser polarization is changed from linear to elliptical, and it becomes maximum for circular polarization. With the aid of a microscopic theory and a detailed analysis of the measured spectra, we reveal that such anomalous enhancement encodes the characteristic topology of the band structure that originates from the interplay of strong spin-orbit coupling and time-reversal symmetry protection. Our study reveals a new platform for chiral strong-field physics and presents a novel, contact-free, all-optical approach for the spectroscopy of topological insulators. The implications are in ultrafast probing of topological phase transitions, light-field driven dissipationless electronics, and quantum computation.
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Submitted 30 September, 2021;
originally announced September 2021.
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Charge-carrier behavior in Ba-, Sr- and Yb-filled CoSb$_3$: NMR and transport studies
Authors:
Yefan Tian,
Ali A. Sirusi,
Sedat Ballikaya,
Nader Ghassemi,
Ctirad Uher,
Joseph H. Ross, Jr
Abstract:
We report $^{59}$Co NMR and transport measurements on $n$-type filled skutterudites Ba$_x$Yb$_y$Co$_4$Sb$_{12}$ and $A$$_x$Co$_4$Sb$_{12}$ ($A$= Ba, Sr), promising thermoelectric materials. The results demonstrate consistently that a shallow defect level near the conduction band minimum dominates the electronic behavior, in contrast to the behavior of unfilled CoSb$_3$. To analyze the results, we…
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We report $^{59}$Co NMR and transport measurements on $n$-type filled skutterudites Ba$_x$Yb$_y$Co$_4$Sb$_{12}$ and $A$$_x$Co$_4$Sb$_{12}$ ($A$= Ba, Sr), promising thermoelectric materials. The results demonstrate consistently that a shallow defect level near the conduction band minimum dominates the electronic behavior, in contrast to the behavior of unfilled CoSb$_3$. To analyze the results, we modeled the defect as having a single peak in the density of states, occupied at low temperatures due to donated charges from filler atoms. We fitted the NMR shifts and spin-lattice relaxation rates allowing for arbitrary carrier densities and degeneracies. The results provide a consistent picture for the Hall data, explaining the temperature dependence of the carrier concentration. Furthermore, without adjusting model parameters, we calculated Seebeck coefficient curves, which also provide good consistency. In agreement with recently reported computational results, it appears that composite native defects induced by the presence of filler atoms can explain this behavior. These results provide a better understanding of the balance of charge carriers, of crucial importance for designing improved thermoelectric materials.
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Submitted 17 October, 2019;
originally announced October 2019.
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Measurements of Nonequilibrium Interatomic Forces in Photoexcited Bismuth
Authors:
Samuel W. Teitelbaum,
Thomas C. Henighan,
Hanzhe Liu,
Mason P. Jiang,
Diling Zhu,
Matthieu Chollet,
Takahiro Sato,
Éamonn D. Murray,
Stephen Fahy,
Shane O'Mahony,
Trevor P. Bailey,
Ctirad Uher,
Mariano Trigo,
David A. Reis
Abstract:
We determine experimentally the excited-state interatomic forces in photoexcited bismuth. The forces are obtained by a constrained least-squares fit of the excited-state dispersion obtained by femtosecond time-resolved x-ray diffuse scattering to a fifteen-nearest neighbor Born-von Karman model. We find that the observed softening of the zone-center $A_{1g}$ optical mode and transverse acoustic mo…
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We determine experimentally the excited-state interatomic forces in photoexcited bismuth. The forces are obtained by a constrained least-squares fit of the excited-state dispersion obtained by femtosecond time-resolved x-ray diffuse scattering to a fifteen-nearest neighbor Born-von Karman model. We find that the observed softening of the zone-center $A_{1g}$ optical mode and transverse acoustic modes with photoexcitation are primarily due to a weakening of three nearest neighbor forces along the bonding direction. This provides a more complete picture of what drives the partial reversal of the Peierls distortion previously observed in photoexcited bismuth.
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Submitted 20 August, 2019;
originally announced August 2019.
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Direct Measurement of Anharmonic Decay Channels of a Coherent Phonon
Authors:
Samuel W. Teitelbaum,
Tom Henighan,
Yijing Huang,
Hanzhe Liu,
Mason P. Jiang,
Diling Zhu,
Matthieu Chollet,
Takahiro Sato,
Éamonn D. Murray,
Stephen Fahy,
Shane O'Mahony,
Trevor P. Bailey,
Ctirad Uher,
Mariano Trigo,
David A. Reis
Abstract:
We observe anharmonic decay of the photoexcited coherent A1g phonon in bismuth to points in the Brillouin zone where conservation of momentum and energy are satisfied for three-phonon scattering. The decay of a coherent phonon can be understood as a parametric resonance process whereby the atomic displacement periodically modulates the frequency of a broad continuum of modes. This results in energ…
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We observe anharmonic decay of the photoexcited coherent A1g phonon in bismuth to points in the Brillouin zone where conservation of momentum and energy are satisfied for three-phonon scattering. The decay of a coherent phonon can be understood as a parametric resonance process whereby the atomic displacement periodically modulates the frequency of a broad continuum of modes. This results in energy transfer through resonant squeezing of the target modes. Using ultrafast diffuse x-ray scattering, we observe build up of coherent oscillations in the target modes driven by this parametric resonance over a wide range of the Brillouin zone. We compare the extracted anharmonic coupling constant to first principles calculations for a representative decay channel.
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Submitted 20 October, 2017; v1 submitted 5 October, 2017;
originally announced October 2017.
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Unconventional Large Linear Magnetoresistance in Cu$_{2-x}$Te
Authors:
Ali A. Sirusi,
Alexander Page,
Lucia Steinke,
Meigan C. Aronson,
Ctirad Uher,
Joseph H. Ross Jr
Abstract:
We report a large linear magnetoresistance in Cu$_{2-x}$Te, reaching $Δρ/ρ(0)$ = 250\% at 2 K in a 9 T field. This is observed for samples with $x$ in the range 0.13 to 0.22, and the results are comparable to the effects observed in Ag$_2 X$ materials, although in this case the results appear for a much wider range of bulk carrier density. Examining the magnitude vs. crossover field from low-field…
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We report a large linear magnetoresistance in Cu$_{2-x}$Te, reaching $Δρ/ρ(0)$ = 250\% at 2 K in a 9 T field. This is observed for samples with $x$ in the range 0.13 to 0.22, and the results are comparable to the effects observed in Ag$_2 X$ materials, although in this case the results appear for a much wider range of bulk carrier density. Examining the magnitude vs. crossover field from low-field quadratic to high-field linear behavior, we show that models based on classical transport behavior best explain the observed results. The effects are traced to misdirected currents due to topologically inverted behavior in this system, such that stable surface states provide the high mobility transport channels. The resistivity also crosses over to a $T^2$ dependence in the temperature range where the large linear MR appears, an indicator of electron-electron interaction effects within the surface states. Thus this is an example of a system in which these interactions dominate the low-temperature behavior of the surface states.
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Submitted 23 March, 2017;
originally announced March 2017.
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Surface vibrational modes of the topological insulator Bi$_2$Se$_3$ observed by Raman spectroscopy
Authors:
H. -H. Kung,
M. Salehi,
I. Boulares,
A. F. Kemper,
N. Koirala,
M. Brahlek,
P. Lošťák,
C. Uher,
R. Merlin,
X. Wang,
S. -W. Cheong,
S. Oh,
G. Blumberg
Abstract:
We present polarization resolved Raman scattering study of surface vibration modes in the topological insulator Bi$_2$Se$_3$ single crystal and thick films. Besides the four Raman active bulk phonons, we observed four additional modes with much weaker intensity and slightly lower energy than the bulk counterparts. Using symmetry analysis, we assigned these additional modes to out-of-plane surface…
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We present polarization resolved Raman scattering study of surface vibration modes in the topological insulator Bi$_2$Se$_3$ single crystal and thick films. Besides the four Raman active bulk phonons, we observed four additional modes with much weaker intensity and slightly lower energy than the bulk counterparts. Using symmetry analysis, we assigned these additional modes to out-of-plane surface phonons. Comparing with first principle calculations, we conclude that the appearance of these modes is due to $c$-axis lattice distortion and van der Waals gap expansion near the crystal surface. Two of the surface modes at 60 and 173 cm$^{-1}$ are associated with Raman active $A_{1g}$ bulk phonon modes, the other two at 136 and 158 cm$^{-1}$ are associated with infrared active bulk phonons with $A_{2u}$ symmetry. The latter become Raman allowed due to reduction of crystalline symmetry from $D_{3d}$ in the bulk to $C_{3v}$ on the crystal surface. In particular, the 158 cm$^{-1}$ surface phonon mode shows a Fano lineshape under resonant excitation, suggesting interference in the presence of electron-phonon coupling of the surface excitations.
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Submitted 9 June, 2017; v1 submitted 17 November, 2016;
originally announced November 2016.
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Suppressed magnetic circular dichroism and valley-selective magneto-absorption due to the effective mass anisotropy in bismuth
Authors:
Pieter J. de Visser,
Julien Levallois,
Michaël K. Tran,
Jean-Marie Poumirol,
Ievgeniia O. Nedoliuk,
Jérémie Teyssier,
Ctirad Uher,
Dirk van der Marel,
Alexey B. Kuzmenko
Abstract:
We have measured the far-infrared reflectivity and Kerr angle spectra on a high-quality crystal of pure semimetallic bismuth as a function of magnetic field, from which we extract the conductivity for left- and right handed circular polarisations. The high spectral resolution allows us to separate the intraband Landau level transitions for electrons and holes. The hole transition exhibits 100% mag…
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We have measured the far-infrared reflectivity and Kerr angle spectra on a high-quality crystal of pure semimetallic bismuth as a function of magnetic field, from which we extract the conductivity for left- and right handed circular polarisations. The high spectral resolution allows us to separate the intraband Landau level transitions for electrons and holes. The hole transition exhibits 100% magnetic circular dichroism, it appears only for one polarisation as expected for a circular cyclotron orbit. However the dichroism for electron transitions is reduced to only $13\pm 1$%, which is quantitatively explained by the large effective mass anisotropy of the electron pockets of the Fermi surface. This observation is a signature of the mismatch between the metric experienced by the photons and the electrons. It allows for a contactless measurement of the effective mass anisotropy and provides a direction towards valley polarised magneto-optical pumping with elliptically polarised light.
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Submitted 2 August, 2016; v1 submitted 30 May, 2016;
originally announced May 2016.
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Understanding the role and interplay of heavy hole and light hole valence bands in the thermoelectric properties of PbSe
Authors:
Thomas C. Chasapis,
Yeseul Lee,
Euripides Hatzikraniotis,
Konstantinos M. Paraskevopoulos,
Hang Chi,
Ctirad Uher,
Mercouri G. Kanatzidis
Abstract:
The thermoelectric properties of PbSe have significantly improved in recent years reaching figures of merit ZT 1.6. The transport properties of the hole doped high temperature thermoelectric material PbSe are particularly interesting and play a key role in this. Here they were analyzed over a wide temperature and hole concentration ranges. The special features observed in the variation of the expe…
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The thermoelectric properties of PbSe have significantly improved in recent years reaching figures of merit ZT 1.6. The transport properties of the hole doped high temperature thermoelectric material PbSe are particularly interesting and play a key role in this. Here they were analyzed over a wide temperature and hole concentration ranges. The special features observed in the variation of the experimental Seebeck coefficient, and Hall coefficient can be accounted for within the framework of a two band model. Two valence bands separated by a temperature dependent energy offset are considered. The extremum of the light hole band has a density of states mass 0.27mo at room temperature. It is non-parabolic and anisotropic and can be described by the Kane model. The extremum of the heavy hole band is isotropic and parabolic with a much larger density of states mass 2.5mo. We find that for heavily doped compositions the high mass band contributes the Seebeck coefficient even at room temperature. With rising temperature holes are transferred from the light hole to the heavy hole branch giving rise to the anomalous temperature dependent Hall coefficient which is found peaked near 650 K.
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Submitted 3 February, 2015;
originally announced February 2015.
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Direct measurement of time-dependent density-density correlations in a solid through the acoustic analog of the dynamical Casimir effect
Authors:
M. Trigo,
M. Fuchs,
J. Chen,
M. P. Jiang,
M. E. Kozina,
G. Ndabashimiye,
M. Cammarata,
G. Chien,
S. Fahy,
D. M. Fritz,
K. Gaffney,
S. Ghimire,
A. Higginbotham,
S. L. Johnson,
J. Larsson,
H. Lemke,
A. M. Lindenberg,
F. Quirin,
K. Sokolowski-Tinten,
C. Uher,
J. S. Wark,
D. Zhu,
D. A. Reis
Abstract:
The macroscopic characteristics of a solid, such as its thermal, optical or transport properties are determined by the available microscopic states above its lowest energy level. These slightly higher quantum states are described by elementary excitations and dictate the response of the system under external stimuli. The spectrum of these excitations, obtained typically from inelastic neutron and…
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The macroscopic characteristics of a solid, such as its thermal, optical or transport properties are determined by the available microscopic states above its lowest energy level. These slightly higher quantum states are described by elementary excitations and dictate the response of the system under external stimuli. The spectrum of these excitations, obtained typically from inelastic neutron and x-ray scattering, is the spatial and temporal Fourier transform of the density-density correlation function of the system, which dictates how a perturbation propagates in space and time. As frequency-domain measurements do not generally contain phase information, time-domain measurements of these fluctuations could yield a more direct method for investigating the excitations of solids and their interactions both in equilibrium and far-from equilibrium. Here we show that the diffuse scattering of femtosecond x-ray pulses produced by a free electron laser (FEL) can directly measure these density-density correlations due to lattice vibrations in the time domain. We obtain spectroscopic information of the lattice excitations with unprecedented momentum- and frequency- resolution, without resolving the energy of the outgoing photon. Correlations are created via an acoustic analog of the dynamical Casimir effect, where a femtosecond laser pulse slightly quenches the phonon frequencies, producing pairs of squeezed phonons at momenta +q and -q. These pairs of phonons manifest as macroscopic, time-dependent coherences in the displacement correlations that are then probed directly by x-ray scattering. Since the time-dependent correlations are preferentially created in regions of strong electron-phonon coupling, the time-resolved approach is natural as a spectroscopic tool of low energy collective excitations in solids, and their microscopic interactions, both in linear response and beyond.
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Submitted 15 January, 2013;
originally announced January 2013.
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Free-carrier relaxation and lattice heating in photoexcited bismuth thin films
Authors:
Y. M. Sheu,
Y. J. Chien,
C. Uher,
S. Fahy,
D. A. Reis
Abstract:
We report ultrafast surface pump and interface probe experiments on photoexcited carrier transport across single crystal bismuth films on sapphire. The film thickness is sufficient to separate carrier dynamics from lattice heating and strain, allowing us to investigate the time-scales of momentum relaxation, heat transfer to the lattice and electron-hole recombination. The measured electron-hole (…
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We report ultrafast surface pump and interface probe experiments on photoexcited carrier transport across single crystal bismuth films on sapphire. The film thickness is sufficient to separate carrier dynamics from lattice heating and strain, allowing us to investigate the time-scales of momentum relaxation, heat transfer to the lattice and electron-hole recombination. The measured electron-hole ($e-h$) recombination time is 12--26 ps and ambipolar diffusivity is 18--40 cm$^{2}$/s for carrier excitation up to $\sim 10^{19} \text{cm}^{-3}$. By comparing the heating of the front and back sides of the film, we put lower limits on the rate of heat transfer to the lattice, and by observing the decay of the plasma at the back of the film, we estimate the timescale of electron-hole recombination. We interpret each of these timescales within a common framework of electron-phonon scattering and find qualitative agreement between the various relaxation times observed. We find that the carrier density is not determined by the $e-h$ plasma temperature after a few picoseconds. The diffusion and recombination become nonlinear with initial excitation $\gtrsim 10^{20} \text{cm}^{-3}$.
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Submitted 16 November, 2012;
originally announced November 2012.
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High temperature charge and thermal transport properties of the n-type thermoelectric material PbSe
Authors:
John Androulakis,
Duck-Young Chung,
Xianli Su,
Li Zhang,
Ctirad Uher,
Thomas C. Hassapis,
Euripides Hatzikraniotis,
Konstantinos M. Paraskevopoulos,
Mercouri G. Kanatzidis
Abstract:
We present a detailed study of the charge transport, optical reflectivity, and thermal transport properties of n-type PbSe crystals. A strong scattering, mobility-limiting mechanism was revealed to be at play at temperatures above 500 K. The mechanism is indicative of complex electron-phonon interactions that cannot be explained by conventional acoustical phonon scattering alone. We applied the fi…
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We present a detailed study of the charge transport, optical reflectivity, and thermal transport properties of n-type PbSe crystals. A strong scattering, mobility-limiting mechanism was revealed to be at play at temperatures above 500 K. The mechanism is indicative of complex electron-phonon interactions that cannot be explained by conventional acoustical phonon scattering alone. We applied the first order non-parabolicity approximation to extract the density of states effective mass as a function of doping both at room temperature and at 700 K. The results are compared to those of a parabolic band model and in the light of doping dependent studies of the infrared optical reflectivity. The thermal conductivity behavior as a function of temperature shows strong deviation from the expected Debye-Peierls high temperature behavior (umklapp dominated) indicating an additional heat carrying channel, which we associate with optical phonon excitations. The correlation of the thermal conductivity observations to the high temperature carrier mobility behavior is discussed. The thermoelectric figure of merit exhibits a promising value of ~0.8 at 700K at 1.5 x 10^{19}$ cm^-3.
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Submitted 10 August, 2011;
originally announced August 2011.
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Thermoelectric enhancement in PbTe with K, Na co-doping from tuning the interaction of the light and heavy hole valence bands
Authors:
John Androulakis,
Iliya Todorov,
Duck-Young Chung,
Sedat Ballikaya,
Guoyu Wang,
Ctirad Uher,
Mercouri Kanatzidis
Abstract:
The effect of K and K-Na substitution for Pb atoms in the rock salt lattice of PbTe was investigated to test a hypothesis for development of resonant states in the valence band that may enhance the thermoelectric power. We combined high temperature Hall-effect, electrical conductivity and thermal conductivity measurements to show that K-Na co-doping do not form resonance states but2 can control th…
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The effect of K and K-Na substitution for Pb atoms in the rock salt lattice of PbTe was investigated to test a hypothesis for development of resonant states in the valence band that may enhance the thermoelectric power. We combined high temperature Hall-effect, electrical conductivity and thermal conductivity measurements to show that K-Na co-doping do not form resonance states but2 can control the energy difference of the maxima of the two primary valence sub-bands in PbTe. This leads to an enhanced interband interaction with rising temperature and a significant rise in the thermoelectric figure of merit of p-type PbTe. The experimental data can be explained by a combination of a single and two-band model for the valence band of PbTe depending on hole density that varies in the range of 1-15 x 10^19 cm^-3.
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Submitted 9 July, 2010;
originally announced July 2010.
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Phase diagram of bismuth in the extreme quantum limit
Authors:
Huan Yang,
Benoit Fauque,
Liam Malone,
Arlei B. Antunes,
Zengwei Zhu,
Ctirad Uher,
Kamran Behnia
Abstract:
Elemental bismuth provides a rare opportunity to explore the fate of a three-dimensional gas of highly mobile electrons confined to their lowest Landau level. Coulomb interaction, neglected in the band picture, is expected to become significant in this extreme quantum limit with poorly understood consequences. Here, we present a study of the angular-dependent Nernst effect in bismuth, which establ…
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Elemental bismuth provides a rare opportunity to explore the fate of a three-dimensional gas of highly mobile electrons confined to their lowest Landau level. Coulomb interaction, neglected in the band picture, is expected to become significant in this extreme quantum limit with poorly understood consequences. Here, we present a study of the angular-dependent Nernst effect in bismuth, which establishes the existence of ultraquantum field scales on top of its complex single-particle spectrum. Each time a Landau level crosses the Fermi level, the Nernst response sharply peaks. All such peaks are resolved by the experiment and their complex angular-dependence is in very good agreement with the theory. Beyond the quantum limit, we resolve additional Nernst peaks signaling a cascade of additional Landau sub-levels caused by electron interaction.
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Submitted 28 July, 2010; v1 submitted 12 April, 2010;
originally announced April 2010.
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Low temperature ferromagnetic properties of the diluted magnetic semiconductor Sb2-xCrxTe3
Authors:
J. S. Dyck,
C. Drasar,
P. Lostak,
C. Uher
Abstract:
We report on magnetic and electrical transport properties of Sb2-xCrxTe3 single crystals with 0 <= x <= 0.095 over temperatures from 2 K to 300 K. A ferromagnetic state develops in these crystals at low temperatures with Curie temperatures that are proportional to x (for x > 0.014), attaining a maximum value of 20 K for x = 0.095. Hysteresis below TC for applied field parallel to the c-axis is o…
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We report on magnetic and electrical transport properties of Sb2-xCrxTe3 single crystals with 0 <= x <= 0.095 over temperatures from 2 K to 300 K. A ferromagnetic state develops in these crystals at low temperatures with Curie temperatures that are proportional to x (for x > 0.014), attaining a maximum value of 20 K for x = 0.095. Hysteresis below TC for applied field parallel to the c-axis is observed in both magnetization and Hall effect measurements. Magnetic as well as transport data indicate that Cr takes the 3+ (3d3) valence state, substituting for antimony in the host lattice structure, and does not significantly affect the background hole concentration. Analysis of the anomalous Hall effect reveals that skew scattering is responsible for its presence. These results broaden the scope of ferromagnetism in the V2-VI3 diluted magnetic semiconductors (DMS) and in ferromagnetic DMS structures generally
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Submitted 15 September, 2004;
originally announced September 2004.