共查询到20条相似文献,搜索用时 0 毫秒
1.
P. T. Coleridge P. Zawadzki A. S. Sachrajda R. L. Williams Y. Feng 《Physica E: Low-dimensional Systems and Nanostructures》2000,6(1-4)
Magnetoresistance measurements are presented for a strained p-SiGe quantum well sample where the density is varied through the B=0 metal–insulator transition. The close relationship between this transition, the high-field Hall insulator transition and the filling factor
insulating state is demonstrated. 相似文献
2.
Bongjin Simon Mun Kai Chen Youngchul Leem Catherine Dejoie Nobumichi Tamura Martin Kunz Zhi Liu Michael E. Grass Changwoo Park Joonseok Yoon Y. Yvette Lee Honglyoul Ju 《固体物理学:研究快报》2011,5(3):107-109
VO2 single crystals with unprecedented quality, exhibiting a first‐order metal–insulator transition (MIT) at 67.8 °C and an insulator –insulator transition (IIT) at ~49 °C, are grown using a self‐flux evaporation method. Using synchrotron‐based X‐ray microdiffraction analysis, it is shown that the IIT is related to a structural phase transition (SPT) from the monoclinic M2 phase to the M1 phase upon heating while the MIT occurs together with a SPT of M1 to the rutile R phase. All previous reports have shown that VO2 exists in the M1 phase at room temperature in contrast to the M2 phase observed in this work. We suggest that internal strain inside single crystal VO2 may generate the previously unobserved IIT and the unusual room temperature structure. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
3.
Joon Sung Lee Sang Keun Seung Seung Ran Lee Jung‐Won Chang Hyunho Noh Lkhagvasuren Baasandorj Hyun Sup Shin Seung‐Bo Shim Jonghyun Song Jinhee Kim 《固体物理学:研究快报》2012,6(12):472-474
We studied the electrical conduction in the LaAlO3/SrTiO3 (LAO/STO) interface electron system with a sub‐critical LAO layer thickness of ~3.5 unit cells (uc). It was found that the true dividing point between metallic and insulating behaviour without gating lies near the LAO thickness of 3.5 uc. Our marginally metallic 3.5 uc sample showed a sharp transition to insulating state at temperatures which strongly depended on the applied negative back‐gate voltage. The superior gate‐controllability of the sample was attributed to its sheet carrier density which was an order of magnitude lower than those of conducting LAO/STO samples with 4 uc or more of LAO layers. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
4.
Bongjin Simon Mun Joonseok Yoon Sung-Kwan Mo Kai Chen Nobumichi Tamura Catherine Dejoie 《Phase Transitions》2013,86(10):941-946
The metal insulator transition (MIT) characteristics of macro-size single-domain VO2 crystal were investigated. At the MIT, the VO2 crystal exhibited a rectangular shape hysteresis curve, a large change in resistance between the insulating and the metallic phases, in the order of ~105, and a small transition width (i.e. temperature difference before and after MIT) as small as 10?3°C. These MIT characteristics of the VO2 crystals are discussed in terms of phase boundary motion and the possibility of controlling the speed of the phase boundary, with change in size of crystal, is suggested. 相似文献
5.
Alexander Pergament 《Phase Transitions》2013,86(3):159-168
On the basis of the Ashcroft empty core model potential, the equation for the constant of Coulomb interaction in the theory of excitonic insulator is modified. It is shown that in this case the dependence of the energy gap width on the charge carrier density obeys the Mott criterion in the limit of low densities. The conformity of the theory with some experimental data concerning metal–insulator phase transitions in doped semiconductors and transition metal compounds is discussed. 相似文献
6.
Observation of insulating–insulating monoclinic structural transition in macro‐sized VO2 single crystals [Phys. Status Solidi RRL 5, No. 3, R107–R109 (2011)] 下载免费PDF全文
Bongjin Simon Mun Kai Chen Youngchul Leem Catherine Dejoie Nobumichi Tamura Martin Kunz Zhi Liu Michael E. Grass Changwoo Park Joonseok Yoon Y. Yvette Lee Honglyoul Ju 《固体物理学:研究快报》2015,9(3):206-206
In our article, we reported the observation of monoclinic M2 to M1 structural phase transition in VO2 single crystal near the temperature of ~49 °C. However, the re‐examination of Laue patterns reveals that previously defined monoclinic M1 and M2 phases can be interpreted as monoclinic M2 and triclinic T phases instead. Careful experimental geometry calibration and further refinement of the lattice parameter ratios and angles show that monoclinic M2 and triclinic T phases fit better with the experimental data. On the other hand, our previous misidentification of the insulating phases does NOT affect the conclusions of our article. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim) 相似文献
7.
We study the superfluid to Mott‐insulator transition of bosons in an optical anisotropic lattice by employing the Bose‐Hubbard model living on a two‐dimensional lattice with anisotropy parameter κ. The compressible superfluid state and incompressible Mott‐insulator (MI) lobes are efficiently described analytically, using the quantum U(1) rotor approach. The ground state phase diagram showing the evolution of the MI lobes is quantified for arbitrary values of κ, corresponding to various kind of lattices: from square, through rectangular to almost one‐dimensional. 相似文献
8.
Thomas Hrmann Georg Pillwein Gerhard Brunthaler 《Physica E: Low-dimensional Systems and Nanostructures》2006,34(1-2):236
The dipole trap model can explain many features of the metallic behavior in gated high-mobility silicon-inversion layers. We have performed numerical calculations of the resistivity in order to drop several restrictions of former analytical considerations. The effect of a limited spatial extent and of energetical distribution broadening of trap states is discussed in this work. 相似文献
9.
R. D. Jggi M. von Waldkirch T. Heinzel E. Ribeiro K. Ensslin G. Medeiros-Ribeiro P. M. Petroff 《Physica E: Low-dimensional Systems and Nanostructures》2000,6(1-4)
A metal–insulator transition at zero magnetic field is observed in Ga[Al]As-heterostructures where a high density of self-assembled InAs-quantum dots is located in the region of the two-dimensional electron gas (2DEG). This transition occurs only in samples with high dot densities. In contrast to other two-dimensional systems showing a metallic phase the Coulomb energy is comparable to the kinetic energy in our systems. Measurements in perpendicular fields reveal that the resistivity at B=0 is composed of several contributions. In the metallic regime a weak localization peak is superposed on top of a broad negative magnetoresistivity. In the insulating regime, the weak localization peak at B=0 develops into a very pronounced negative magnetoresistivity with decreasing electron density. Pronounced, almost B-periodic oscillations in the magnetoresistivity are observed in addition to universal conductance fluctuations. 相似文献
10.
Metal–Insulator transition using an exact two-dimensional (2D) dielectric function is investigated for a shallow donor in an isolated well of a GaAs/Ga1−xAlsAs superlattice system within the effective mass approximation. Vanishing of the donor ionization energy as a function of well width and the donor concentration suggests that a phase transition is not possible even below a well width of 10 Å, supporting the scaling theory of localization. The effects of Anderson localization, exchange and correlation in the Hubbard model are included in a simple way. The relationship between the present model and the Mott criterion in terms of Hubbard model is also brought out. The critical concentration appears to be enhanced when a random distribution of impurities is considered. The limiting behaviour of the well width for a quantum 2D well is brought out. A simple expression is derived for a Mott constant in 2D, a*Nc1/2 exp (9.86 exp (−L/a*))=0.123, where Nc is the critical concentration per area. Results are compared with the existing data available and discussed in the light of existing literature. 相似文献
11.
B. Lindner G. Pillwein G. Brunthaler J. Ahopelto M. Prunnila 《Physica E: Low-dimensional Systems and Nanostructures》2006,34(1-2):256
The strong resistivity changes in the metallic state of two-dimensional electron systems have recently been assigned to quantum interaction corrections in the ballistic regime. We have performed analysis of Shubnikov–de Haas oscillations on high-mobility silicon inversion layers where we have explicitly taken into account that the back scattering angle has different influence on momentum relaxation and quantum life time. The consistent analysis under the assumption of the ballistic interaction corrections leads to smaller increase of the effective mass with decreasing electron density as usually reported. 相似文献
12.
Thomas Vojta 《Annalen der Physik》2000,9(6):403-440
Quantum phase transitions occur at zero temperature when some non‐thermal control‐parameter like pressure or chemical composition is changed. They are driven by quantum rather than thermal fluctuations. In this review we first give a pedagogical introduction to quantum phase transitions and quantum critical behavior emphasizing similarities with and differences to classical thermal phase transitions. We then illustrate the general concepts by discussing a few examples of quantum phase transitions occurring in electronic systems. The ferromagnetic transition of itinerant electrons shows a very rich behavior since the magnetization couples to additional electronic soft modes which generates an effective long‐range interaction between the spin fluctuations. We then consider the influence of rare regions on quantum phase transitions in systems with quenched disorder, taking the antiferromagnetic transitions of itinerant electrons as a primary example. Finally we discuss some aspects of the metal‐insulator transition in the presence of quenched disorder and interactions. 相似文献
13.
We study numerically the conductance distribution function w(T) for the one‐dimensional Anderson model with random long‐range hopping described by the Power‐law Banded Random Matrix model at criticality. We concentrate on the case of two single‐channel leads attached to the system. We observe a smooth transition from localized to delocalized behavior in the conductance distribution by increasing b, the effective bandwidth of the model. Also, for b < 1 we show that w(ln T/Ttyp) is scale invariant, where Ttyp = exp 〈 ln T 〉 is the typical value of T. Moreover, we find that for T < Ttyp, w(ln T/Ttyp) shows a universal behavior proportional to (T/Ttyp)‐1/2. 相似文献
14.
C. Piamonteze H. C. N. Tolentino A. Y. Ramos N. E. Massa J. A. Alonso M. J. Martinez-Lope M. T. Casais 《Physica B: Condensed Matter》2002,320(1-4):71-74
Rare earth nickel oxide perovskites (RNiO3, R=rare earth) have, except for LaNiO3, a metal–insulator (MI) phase transition as temperature decreases. The transition temperature (TMI) increases as the R-ion becomes smaller. They also present, at low temperatures, a complex antiferromagnetic order. For lighter R-ions (e.g. Pr and Nd), the antiferromagnetic transition temperature (TN) is close to TMI, while for heavier R-ions (e.g. Eu, Sm), TMI and TN are very far apart, suggesting that the magnetic and electronic behaviors are not directly coupled. Even though Ni3+ is a Jahn–Teller ion, no distortion in the NiO6 octahedra was found for RNiO3 perovskites with R=Pr, Nd, Sm and Eu. In this work we have measured EXAFS at Ni K edge for samples of PrNiO3, NdNiO3 and EuNiO3. The Fourier transform spectra for the three samples show a clear splitting in the first peak at the insulating phase. This splitting corresponds to two or more different Ni–O distances. This indicates that there is either a distortion in the NiO6 octahedra or there are two different Ni sites at the insulating phase. 相似文献
15.
The density of states of Dirac fermions with a random mass on a two‐dimensional lattice is considered. We give the explicit asymptotic form of the single‐electron density of states as a function of both energy and (average) Dirac mass, in the regime where all states are localized. We make use of a weak‐disorder expansion in the parameter g/m2, where g is the strength of disorder and m the average Dirac mass for the case in which the evaluation of the (supersymmetric) integrals corresponds to non‐uniform solutions of the saddle point equation. The resulting density of states has tails which deviate from the typical pure Gaussian form by an analytic prefactor. 相似文献
16.
We examined the temperature-dependent electrical, optical, and structural properties of VO2 on ZnO nanorods with different lengths in the temperature range from 30 to 100 °C. ZnO nanorods with a uniform length were grown on Al2O3 substrates using a metal organic chemical vapor deposition, and subsequently, VO2 was ex-situ deposited on ZnO nanorods/Al2O3 templates using a sputtering deposition. The optical properties of the VO2/ZnO nanorods were measured simultaneously with direct current (DC) resistance using the reflectivity of an infrared (IR) laser beam with a wavelength of 790 nm. The local structural properties around V atoms of VO2/ZnO nanorods were simultaneously measured with the DC resistance using x-ray absorption fine structure at the V K edge. Direct comparison of the temperature-dependent resistance, IR reflectivity, and local structure reveals that an optical phase transition first occurs, a structural phase transition follows, and an insulator-to-metal transition finally appears during heating. 相似文献
17.
Przemek J. Bock Pavel Cheben Aitor V. Velasco Jens H. Schmid Andr Delge Mirosaw Florjaczyk Jean Lapointe Dan‐Xia Xu Martin Vachon Siegfried Janz María L. Calvo 《Laser \u0026amp; Photonics Reviews》2013,7(6):L67-L70
A planar waveguide Fourier‐transform spectrometer with densely arrayed Mach‐Zehnder interferometers is demonstrated. Subwavelength gratings are used to produce an optical path difference without waveguide bends. The fabricated device comprises of an array of 32 Mach‐Zehnder interferometers, which produce a spatial interferogram without any moving parts, yielding a spectral resolution of 50 pm and a free‐spectral range of 0.78 nm. As a result of similar propagation losses in subwavelength grating waveguides and conventional strip waveguides, loss imbalance is minimized and high interferometic extinction ratio of −25 to −30 dB is obtained. Furthermore, phase and amplitude errors arising from normal fabrication variation are compensated by the spectral retrieval process using calibration measurements. 相似文献
18.
Siham Refki Shinji Hayashi Hidekazu Ishitobi Dmitry V. Nesterenko Anouar Rahmouni Yasushi Inouye Zouheir Sekkat 《Annalen der Physik》2018,530(4)
Optical sensors based on surface plasmons have attracted much attention over the past decades owing to the wealth of applications in bio‐ and chemical and gas sensing. In surface plasmon resonance sensors, a single metal layer is commonly used, but its resolution is limited because of broad resonances. In this context, we have developed a sensor chip based on a stack of metals and a dielectric, e.g. a metal‐insulator‐metal structure, consisting of a thick insulator layer sandwiched by metal layers, that exhibits a sharp resonance due to the excitation of surface plasmon polaritons hybrid modes. We have performed both experiments and theoretical simulations to estimate the enhancement of the sensitivity of such a structure. By changing the refractive index of an aqueous solution of glucose on top of the sensor chip, we found that the use of a metal‐insulator‐metal structure improves the figure of merit of the sensor 7.5 times compared to that of a conventional surface plasmon resonance sensor chip. 相似文献
19.
20.
The effect of benzo‐annelation on intermolecular hydrogen bond and proton transfer of 2‐methyl‐3‐hydroxy‐4(1H)‐quinolone in methanol: A TD‐DFT study 下载免费PDF全文
Yanliang Zhao Meishan Wang Panwang Zhou Chuanlu Yang Xiaoguang Ma Zhe Tang Dongshuai Bao 《Journal of Physical Organic Chemistry》2018,31(5)
Excited‐state intermolecular or intramolecular proton transfer (ESIPT) reaction has important potential applications in biological probes. In this paper, the effect of benzo‐annelation on intermolecular hydrogen bond and proton transfer reaction of the 2‐methyl‐3‐hydroxy‐4(1H)‐quinolone (MQ) dye in methanol solvent is investigated by the density functional theory and time‐dependent density functional theory approaches. Both the primary structure parameters and infrared vibrational spectra analysis of MQ and its benzo‐analogue 2‐methyl‐3‐hydroxy‐4(1H)‐benzo‐quinolone (MBQ) show that the intermolecular hydrogen bond O1―H2?O3 significantly strengthens in the excited state, whereas another intermolecular hydrogen bond O3―H4?O5 weakens slightly. Simulated electron absorption and fluorescence spectra are agreement with the experimental data. The noncovalent interaction analysis displays that the intermolecular hydrogen bonds of MQ are obviously stronger than that of MBQ. Additionally, the energy profile analysis via the proton transfer reaction pathway illustrates that the ESIPT reaction of MBQ is relatively harder than that of MQ. Therefore, the effect of benzo‐annelation of the MQ dye weakens the intermolecular hydrogen bond and relatively inhibits the proton transfer reaction. 相似文献