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Dyakonov-Perel-like Orbital and Spin Relaxations in Centrosymmetric Systems
Authors:
Jeonghun Sohn,
Jongjun M. Lee,
Hyun-Woo Lee
Abstract:
The Dyakonov-Perel (DP) mechanism of spin relaxation has long been considered irrelevant in centrosymmetric systems since it was developed originally for non-centrosymmetric ones. We investigate whether this conventional understanding extends to the realm of orbital relaxation, which has recently attracted significant attention. Surprisingly, we find that orbital relaxation in centrosymmetric syst…
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The Dyakonov-Perel (DP) mechanism of spin relaxation has long been considered irrelevant in centrosymmetric systems since it was developed originally for non-centrosymmetric ones. We investigate whether this conventional understanding extends to the realm of orbital relaxation, which has recently attracted significant attention. Surprisingly, we find that orbital relaxation in centrosymmetric systems exhibits the DP-like behavior in the weak scattering regime. Moreover, the DP-like orbital relaxation can make the spin relaxation in centrosymmetric systems DP-like through the spin-orbit coupling. We also find that the DP-like orbital and spin relaxations are anisotropic even in materials with high crystal symmetry (such as face-centered cubic structure) and may depend on the orbital and spin nature of electron wavefunctions.
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Submitted 17 April, 2024;
originally announced April 2024.
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Quantum Bit Behavior of Pinned Fluxes on Volume Defects in a Superconductor
Authors:
H. B. Lee,
G. C. Kim,
Byeong-Joo Kim,
Young Jin Sohn,
Y. C. Kim
Abstract:
We studied a qubit based on flux-pinning effects in $Δ$H=$Δ$B region of a superconductor. When volume defects are many enough in a superconductor, $Δ$H=$Δ$B region on M-H curve is formed, which is the region that increased applied magnetic field ($Δ$H) is the same as increasing magnetic induction ($Δ$B). Magnetization (M) is constant in the region by 4$π$M = B - H. Here we show that the behavior o…
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We studied a qubit based on flux-pinning effects in $Δ$H=$Δ$B region of a superconductor. When volume defects are many enough in a superconductor, $Δ$H=$Δ$B region on M-H curve is formed, which is the region that increased applied magnetic field ($Δ$H) is the same as increasing magnetic induction ($Δ$B). Magnetization (M) is constant in the region by 4$π$M = B - H. Here we show that the behavior of fluxes in $Δ$H=$Δ$B region can be a candidate of qubit. Pinned fluxes on volume defects would move as a bundle in the region by repeating flux-pinning and pick-out depinning process from the surface to the center of the superconductor. During the process, magnetic fluxes would exist as one of states that are flux-pinning state at volume defects and pick-out depinning state in which fluxes are moving in the superconductor. A difference of diamagnetic property occurs between pinning state at volume defects and depinning state from the volume defects. Thus, diamagnetic properties of the superconductor would oscillate in $Δ$H=$Δ$B region and the behavior would be observed in M-H curve. The oscillation can be used for qubit by setting the pinning state at volume defects as $\ket{1}$ and the depinned state as $\ket{0}$. This method can operate at higher temperatures than that of using Josephson Junctions. In addition, it is expected that the device is quite simple and decoherences can be almost negligible.
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Submitted 16 January, 2022;
originally announced January 2022.
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PCM-net: A refractive index database of chalcogenide phase change materials for tunable nanophotonic device modelling
Authors:
Hyun Jung Kim,
Jung-woo Sohn,
Nina Hong,
Calum Williams,
William Humphreys
Abstract:
Recently, chalcogenide glass based phase change materials (PCMs) have shown utility as a tuning material for a range of nanophotonic devices. Owing to their low loss, ultrafast switching speeds and wide waveband operation, PCMs are integrated in an increasing number of next generation tunable components, including integrated photonic switches, metasurface optics and tunable spectral filters. Nonet…
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Recently, chalcogenide glass based phase change materials (PCMs) have shown utility as a tuning material for a range of nanophotonic devices. Owing to their low loss, ultrafast switching speeds and wide waveband operation, PCMs are integrated in an increasing number of next generation tunable components, including integrated photonic switches, metasurface optics and tunable spectral filters. Nonetheless, modelling of PCM-based devices is challenging, both in terms of accurate representation of experimentally-derived material properties in different phase states, and standardization of results across the research community. In this work, we introduce PCMnet, an online database of the complex refractive indices of a variety of chalcogenide glass PCMs (such as GeSbTe), as an accessible and indexed repository for data sharing across the PCM community. Refractive indices (n) and extinction coefficients (k) between amorphous and crystalline states are directly extracted from experimentally-derived data in numerous academic research articles, and collated into the material resource database. Due to the inaccuracies associated with our data collection methods, this data is supplemented with additional computationally-generated data, obtained through WVASE, a commercial ellipsometry analysis software package. To demonstrate the utility of PCMnet, we provide a NASA application-driven device optimization example using the optical properties of PCMs collected with our database. We anticipate the database providing great use to the PCM community and coordinated research efforts enabled by PCMnet will promote the shared repository for the selection of appropriate PCMs for tunable nanophotonic device design for a range of applications.
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Submitted 28 December, 2020;
originally announced December 2020.
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A highly integrated, stand-alone photoelectrochemical device for large-scale solar hydrogen production
Authors:
Minoh Lee,
Bugra Turan,
Jan-Philipp Becker,
Katharina Welter,
Benjamin Klingebiel,
Elmar Neumann,
Yoo Jung Sohn,
Tsvetelina Merdzhanova,
Thomas Kirchartz,
Friedhelm Finger,
Uwe Rau,
Stefan Haas
Abstract:
Although photoelectrochemical water splitting is likely to be an important and powerful tool to provide environmentally friendly hydrogen, most developments in this field have been conducted on a laboratory scale so far. In order for the technology to make a sizeable impact on the energy transition, scaled up devices made of inexpensive and earth abundant materials must be developed. In this work,…
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Although photoelectrochemical water splitting is likely to be an important and powerful tool to provide environmentally friendly hydrogen, most developments in this field have been conducted on a laboratory scale so far. In order for the technology to make a sizeable impact on the energy transition, scaled up devices made of inexpensive and earth abundant materials must be developed. In this work, we demonstrate a scalable (64 cm2 aperture area) artificial photoelectrochemical device composed of triple-junction thin-film silicon solar cells in conjunction with an electrodeposited bifunctional nickel iron molybdenum water splitting catalyst. Our device shows a solar to hydrogen efficiency of up to 4.67% (5.33% active area) without bias assistance and wire connection. Furthermore, gas separation was enabled by incorporating a membrane in a 3D printed device frame.
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Submitted 30 October, 2019;
originally announced October 2019.
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A pseudo-capacitive chalcogenide-based electrode with dense 1-dimensional nanoarrays for enhanced energy density in asymmetric supercapacitors
Authors:
Young-Woo Lee,
Byung-Sung Kima,
Jong Hong,
Juwon Lee,
Sangyeon Pak,
Hyeon-Sik Jang,
Dongmok Whang,
SeungNam Cha,
Jung Inn Sohn,
Jong Min Kim
Abstract:
To achieve the further development of supercapacitors (SCs), which have intensively received attention as a next-generation energy storage system, the rational design of active electrode materials with electrochemically more favorable structure is one of the most important factors to improve the SC performance with high specific energy and power density. We propose and successfully grow copper sul…
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To achieve the further development of supercapacitors (SCs), which have intensively received attention as a next-generation energy storage system, the rational design of active electrode materials with electrochemically more favorable structure is one of the most important factors to improve the SC performance with high specific energy and power density. We propose and successfully grow copper sulfide (CuS) nanowires (NWs) as a chalcogenide-based electrode material directly on a Cu mesh current collector using the combination of a facile liquid-solid chemical oxidation process and an anion exchange reaction. We found that the as-prepared CuS NWs have well-arrayed structures with nanosized crystal grains, a high aspect ratio and density, as well as a good mechanical and electrical contact to the Cu mesh. The obtained CuS NW based electrodes, with additional binder- and conductive material-free, exhibit a much higher areal capacitance of 378.0 mF/cm2 and excellent cyclability of an approximately 90.2 percentage retention during 2000 charge/discharge cycles due to their unique structural, electrical, and electrochemical properties. Furthermore, for practical SC applications, an asymmetric supercapacitor is fabricated using active carbon as an anode and CuS NWs as a cathode, and exhibits the good capacitance retention of 91% during 2000 charge/discharge processes and the excellent volumetric energy density of 1.11 mW h/cm3 compared to other reported pseudo-capacitive SCs.
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Submitted 15 May, 2019;
originally announced May 2019.
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Resonantly hybridised excitons in moiré superlattices in van der Waals heterostructures
Authors:
Evgeny M. Alexeev,
David A. Ruiz-Tijerina,
Mark Danovich,
Matthew J. Hamer,
Daniel J. Terry,
Pramoda K. Nayak,
Seongjoon Ahn,
Sangyeon Pak,
Juwon Lee,
Jung Inn Sohn,
Maciej R. Molas,
Maciej Koperski,
Kenji Watanabe,
Takashi Taniguchi,
Kostya S. Novoselov,
Roman V. Gorbachev,
Hyeon Suk Shin,
Vladimir I. Fal'ko,
Alexander I. Tartakovskii
Abstract:
Atomically-thin layers of two-dimensional materials can be assembled in vertical stacks held together by relatively weak van der Waals forces, allowing for coupling between monolayer crystals with incommensurate lattices and arbitrary mutual rotation. A profound consequence of using these degrees of freedom is the emergence of an overarching periodicity in the local atomic registry of the constitu…
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Atomically-thin layers of two-dimensional materials can be assembled in vertical stacks held together by relatively weak van der Waals forces, allowing for coupling between monolayer crystals with incommensurate lattices and arbitrary mutual rotation. A profound consequence of using these degrees of freedom is the emergence of an overarching periodicity in the local atomic registry of the constituent crystal structures, known as a moiré superlattice. Its presence in graphene/hexagonal boron nitride (hBN) structures led to the observation of electronic minibands, whereas its effect enhanced by interlayer resonant conditions in twisted graphene bilayers culminated in the observation of the superconductor-insulator transition at magic twist angles. Here, we demonstrate that, in semiconducting heterostructures built of incommensurate MoSe2 and WS2 monolayers, excitonic bands can hybridise, resulting in the resonant enhancement of the moiré superlattice effects. MoSe2 and WS2 are specifically chosen for the near degeneracy of their conduction band edges to promote the hybridisation of intra- and interlayer excitons, which manifests itself through a pronounced exciton energy shift as a periodic function of the interlayer rotation angle. This occurs as hybridised excitons (hX) are formed by holes residing in MoSe2 bound to a twist-dependent superposition of electron states in the adjacent monolayers. For heterostructures with almost aligned pairs of monolayer crystals, resonant mixing of the electron states leads to pronounced effects of the heterostructure's geometrical moiré pattern on the hX dispersion and optical spectrum. Our findings underpin novel strategies for band-structure engineering in semiconductor devices based on van der Waals heterostructures.
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Submitted 12 April, 2019;
originally announced April 2019.
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Imaging of interlayer coupling in van der Waals heterostructures using a bright-field optical microscope
Authors:
Evgeny M. Alexeev,
Alessandro Catanzaro,
Oleksandr V. Skrypka,
Pramoda K. Nayak,
Seongjoon Ahn,
Sangyeon Pak,
Juwon Lee,
Jung Inn Sohn,
Kostya S. Novoselov,
Hyeon Suk Shin,
Alexander I. Tartakovskii
Abstract:
Vertically stacked atomic layers from different layered crystals can be held together by van der Waals forces, which can be used for building novel heterostructures, offering a platform for developing a new generation of atomically thin, transparent and flexible devices. The performance of these devices is critically dependent on the layer thickness and the interlayer electronic coupling, influenc…
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Vertically stacked atomic layers from different layered crystals can be held together by van der Waals forces, which can be used for building novel heterostructures, offering a platform for developing a new generation of atomically thin, transparent and flexible devices. The performance of these devices is critically dependent on the layer thickness and the interlayer electronic coupling, influencing the hybridisation of the electronic states as well as charge and energy transfer between the layers. The electronic coupling is affected by the relative orientation of the layers as well as by the cleanliness of their interfaces. Here, we demonstrate an efficient method for monitoring interlayer coupling in heterostructures made from transition metal dichalcogenides using photoluminescence imaging in a bright-field optical microscope. The colour and brightness in such images are used here to identify mono- and few-layer crystals, and to track changes in the interlayer coupling and the emergence of interlayer excitons after thermal annealing in mechanically exfoliated flakes as well as a function of the twist angle in atomic layers grown by chemical vapour deposition. Material and crystal thickness sensitivity of the presented imaging technique makes it a powerful tool for characterisation of van der Waals heterostructures assembled by a wide variety of methods, using combinations of materials obtained through mechanical or chemical exfoliation and crystal growth.
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Submitted 1 May, 2017; v1 submitted 23 December, 2016;
originally announced December 2016.
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Thermoelectric Signal Enhancement by Reconciling the Spin Seebeck and Anomalous Nernst Effects in Ferromagnet/Non-magnet Multilayers
Authors:
Kyeong-Dong Lee,
Dong-Jun Kim,
Hae Yeon Lee,
Seung-Hyun Kim,
Jong-Hyun Lee,
Kyung-Min Lee,
Jong-Ryul Jeong,
Ki-Suk Lee,
Hyon-Seok Song,
Jeong-Woo Sohn,
Sung-Chul Shin,
Byong-Guk Park
Abstract:
The utilization of ferromagnetic (FM) materials in thermoelectric devices allows one to have a simpler structure and/or independent control of electric and thermal conductivities, which may further remove obstacles for this technology to be realized. The thermoelectricity in FM/non-magnet (NM) heterostructures using an optical heating source is studied as a function of NM materials and a number of…
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The utilization of ferromagnetic (FM) materials in thermoelectric devices allows one to have a simpler structure and/or independent control of electric and thermal conductivities, which may further remove obstacles for this technology to be realized. The thermoelectricity in FM/non-magnet (NM) heterostructures using an optical heating source is studied as a function of NM materials and a number of multilayers. It is observed that the overall thermoelectric signal in those structures which is contributed by spin Seebeck effect and anomalous Nernst effect (ANE) is enhanced by a proper selection of NM materials with a spin Hall angle that matches to the sign of the ANE. Moreover, by an increase of the number of multilayer, the thermoelectric voltage is enlarged further and the device resistance is reduced, simultaneously. The experimental observation of the improvement of thermoelectric properties may pave the way for the realization of magnetic-(or spin-) based thermoelectric devices.
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Submitted 2 April, 2015;
originally announced April 2015.
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Metal Oxide Resistive Memory using Graphene Edge Electrode
Authors:
Seunghyun Lee,
Joon Sohn,
Zizhen Jiang,
Hong-Yu Chen,
H. -S. Philip Wong
Abstract:
The emerging paradigm of abundant-data computing requires real-time analytics on enormous quantities of data collected by a mushrooming network of sensors. Todays computing technology, however, cannot scale to satisfy such big data applications with the required throughput and energy efficiency. The next technology frontier will be monolithically integrated chips with three dimensionally interleav…
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The emerging paradigm of abundant-data computing requires real-time analytics on enormous quantities of data collected by a mushrooming network of sensors. Todays computing technology, however, cannot scale to satisfy such big data applications with the required throughput and energy efficiency. The next technology frontier will be monolithically integrated chips with three dimensionally interleaved memory and logic for unprecedented data bandwidth with reduced energy consumption. In this work, we exploit the atomically thin nature of the graphene edge to assemble a resistive memory stacked in a vertical three dimensional structure. We report some of the lowest power and energy consumption among the emerging non-volatile memories due to an extremely thin electrode with unique properties, low programming voltages, and low current. Circuit analysis of the architecture using experimentally measured device properties show higher storage potential for graphene devices compared that of metal based devices.
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Submitted 20 August, 2015; v1 submitted 9 February, 2015;
originally announced February 2015.
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Decomposing Entropy Productions by Double Control Parameters
Authors:
Jang-il Sohn
Abstract:
In the present work, we study the entropy productions in a system controlled by double control parameters. By introducing a thermal fluctuation part, we solve the problem that the second law of the thermodynamics seems to be violated by the thermal fluctuation near equilibrium in the microscopic levels. Then we define the negative and the compensating entropy productions in the macroscopic levels.
In the present work, we study the entropy productions in a system controlled by double control parameters. By introducing a thermal fluctuation part, we solve the problem that the second law of the thermodynamics seems to be violated by the thermal fluctuation near equilibrium in the microscopic levels. Then we define the negative and the compensating entropy productions in the macroscopic levels.
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Submitted 19 August, 2015; v1 submitted 3 June, 2014;
originally announced June 2014.
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Entropy Production by Logarithmic Decomposition
Authors:
Jang-il Sohn
Abstract:
In statistical physics, entropy is generally logarithm of probability. Therefore, if dynamics is decomposed by log, entropy production should be decomposed properly. In the present work, log-decomposition of dynamics is introduced. By which time evolution operator is logarithmically decomposed into a symmetric operator and an asymmetric factor. Path probability and path entropy production are also…
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In statistical physics, entropy is generally logarithm of probability. Therefore, if dynamics is decomposed by log, entropy production should be decomposed properly. In the present work, log-decomposition of dynamics is introduced. By which time evolution operator is logarithmically decomposed into a symmetric operator and an asymmetric factor. Path probability and path entropy production are also systematically and intuitively decomposed into symmetric and asymmetric parts. From symmetric operator, non-adiabatic entropy production is derived, whereas adiabatic entropy production is from asymmetric factor.
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Submitted 29 April, 2014;
originally announced April 2014.
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Path Entropy Changes in Adiabatic Approximation
Authors:
Jang-il Sohn
Abstract:
By applying adiabatic theorem to a Markovian system, we calculate the adiabatic and diabatic entropy changes along a path. As well known, the total path entropy change is separated into two parts, system and environment entropy changes, $ΔS_{tot} = ΔS_{sys} + ΔS_{env}$. The environment entropy change, $ΔS_{env}$, is divided again into two parts, an adiabatic contribution due to work,…
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By applying adiabatic theorem to a Markovian system, we calculate the adiabatic and diabatic entropy changes along a path. As well known, the total path entropy change is separated into two parts, system and environment entropy changes, $ΔS_{tot} = ΔS_{sys} + ΔS_{env}$. The environment entropy change, $ΔS_{env}$, is divided again into two parts, an adiabatic contribution due to work, $ΔS_{\mathcal{W}}$, and a diabatic contributions due to heat, $ΔS_{\mathcal{Q}}$. In an adiabatic process, total path entropy change is same with the adiabatic path entropy change, $ΔS_{A}$, which is given by sum of system entropy change and adiabatic contribution, $ΔS_{A} = ΔS_{sys} + ΔS_{\mathcal{W}}$. Mathematical form of $ΔS_{A}$ is a type of excess heat entropy change, but $ΔS_{A}$ is due to work. By which, it is shown that the terms adiabatic and non-adiabatic contributions of $ΔS_{na}$ and $ΔS_{a}$ in [Phys. Rev. Lett. {\bf 104}, 090601 (2010)] should be completely switched, $i.e.$ $ΔS_{na} \rightarrow ΔS_{A}$ and $ΔS_{a} \rightarrow ΔS_{\mathcal{Q}}$ in fact.
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Submitted 25 September, 2012; v1 submitted 20 August, 2012;
originally announced August 2012.
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Modeling the mobility with memory
Authors:
Jeehye Choi,
Jang-Il Sohn,
K. -I. Goh,
I. -M. Kim
Abstract:
We study a random walk model in which the jumping probability to a site is dependent on the number of previous visits to the site, as a model of the mobility with memory. To this end we introduce two parameters called the memory parameter alpha and the impulse parameter p. From extensive numerical simulations, we found that various limited mobility patterns such as sub-diffusion, trapping, and log…
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We study a random walk model in which the jumping probability to a site is dependent on the number of previous visits to the site, as a model of the mobility with memory. To this end we introduce two parameters called the memory parameter alpha and the impulse parameter p. From extensive numerical simulations, we found that various limited mobility patterns such as sub-diffusion, trapping, and logarithmic diffusion could be observed. By the memory, a long-ranged directional anti-correlation kinetically-induces anomalous sub-diffusive and trapping behaviors, and transition between them. With random jumps by the impulse parameter, a trapped walker can escape from the trap very slowly, resulting in an ultraslow logarithmic diffusive behavior. Our results suggest that the memory of walker's has-beens can be one mechanism explaining many of empirical characteristics of the mobility of animated objects.
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Submitted 17 June, 2012;
originally announced June 2012.
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Low temperature terahertz spectroscopy of n-InSb through a magnetic field driven metal-insulator transition
Authors:
X. P. A. Gao,
J. Y. Sohn,
S. A. Crooker
Abstract:
We use fiber-coupled photoconductive emitters and detectors to perform terahertz (THz) spectroscopy of lightly-doped n-InSb directly in the cryogenic (1.5 K) bore of a high-field superconducting magnet. We measure transmission spectra from 0.1-1.1 THz as the sample is driven through a metal-insulator transition (MIT) by applied magnetic field. In the low-field metallic state, the data directly r…
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We use fiber-coupled photoconductive emitters and detectors to perform terahertz (THz) spectroscopy of lightly-doped n-InSb directly in the cryogenic (1.5 K) bore of a high-field superconducting magnet. We measure transmission spectra from 0.1-1.1 THz as the sample is driven through a metal-insulator transition (MIT) by applied magnetic field. In the low-field metallic state, the data directly reveal the plasma edge and magneto-plasmon modes. With increasing field, a surprisingly broad band (0.3-0.8 THz) of low transmission appears at the onset of the MIT. This band subsequently collapses and evolves into the sharp 1s -> 2p- transition of electrons `frozen' onto isolated donors in the insulating state.
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Submitted 24 May, 2006; v1 submitted 2 May, 2006;
originally announced May 2006.
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Critical couplings in Crystalline Color superconductivity
Authors:
Deog Ki Hong,
Y. J. Sohn
Abstract:
Solving the Schwinger-Dyson equations, we analyze the pairing of quarks in asymmetric quark matter where quarks have different chemical potentials. We show that in the asymmetric quark matter a crystalline color-superconducting gap opens when the quark coupling is stronger than a critical value. The critical coupling is nonzero, since the infrared divergence is lessened when the momenta of pairi…
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Solving the Schwinger-Dyson equations, we analyze the pairing of quarks in asymmetric quark matter where quarks have different chemical potentials. We show that in the asymmetric quark matter a crystalline color-superconducting gap opens when the quark coupling is stronger than a critical value. The critical coupling is nonzero, since the infrared divergence is lessened when the momenta of pairing quarks are not opposite. The superconducting gaps and the critical couplings are calculated both at high and intermediate densities.
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Submitted 30 June, 2001;
originally announced July 2001.