Topological Superconductivity in Cu(x)Bi(2)Se(3)

A topological superconductor (TSC) is characterized by the topologically protected gapless surface state that is essentially an Andreev bound state consisting of Majorana fermions. While a TSC has not yet been discovered, the doped topological insulator Cu(x)Bi(2)Se(3), which superconducts below ～3 K, has been predicted to possess a topological superconducting state. We report that the point-contact spectra on the cleaved surface of superconducting Cu(x)Bi(2)Se(3) present a zero-bias conductance peak (ZBCP) which signifies unconventional superconductivity. Theoretical considerations of all possible superconducting states help us conclude that this ZBCP is due to Majorana fermions and gives evidence for a topological superconductivity in Cu(x)Bi(2)Se(3). In addition, we found an unusual pseudogap that develops below ～20 K and coexists with the topological superconducting state.     

Methods for the measurement of (1)J(NCalpha) and (2)J(NCalpha) from a simplified 2D (13)C(alpha)-coupled (15)N SE-HSQC spectrum

Two methods for the measurement of (2)J(NCalpha) and (1)J(NCalpha) in (15)N/(13)C-labeled small and medium-size proteins are described. The current approach is based on simplified (13)C(alpha)-coupled (15)N HSQC spectra, where the two (2)J(NCalpha) doublets are separated into two subspectra corresponding to the alpha and beta spin states of the residue's own alpha carbon. The displacement of the two (2)J(NCalpha) doublets between the two subspectra provides an accurate value for (1)J(NCalpha). The alpha/beta filtration is achieved by taking the sum and difference of the recorded complementary in-phase and antiphase J-coupled spectra. J-multiplication is utilized in one of the proposed methods. In this method, an additional coupling evolution period, which is incremented in concert with t(1), is included in the pulse sequence making it possible to scale the peak-to-peak separation.     

Low thermal expansion and broad band photoluminescence of Zr0.1Al1.9Mo2.9V0.1O12

A new material of Zr0.1Al1.9Mo2.9V0.1O12 is synthesized by the traditional solid state synthesis method.The phase transition,coefficient of thermal expansion,and luminescence properties of Zr0.1Al1.9Mo2.9V0.1O12 are explored with Raman spectrometer,dilatometer,and x-ray diffraction(XRD)diffractometer.The results show that the Zr0.1Al1.9Mo2.9V0.1O12 possesses the strong broad-band luminescence characteristics almost in the whole visible region.The sample is crystallized in a monoclinic structure group of P21/a(No.14)crystallized at room temperature(RT).The crystal is changed from monoclinic to orthorhombic structure when the temperature increases to 463 K.The material has very low thermal expansion performance in a wide temperature range.Its excellent low thermal expansion and strong pale green light properties in a wide temperature range suggest its potential applications in light-emitting diode(LED)and other optoelectronic devices.     

The (29)Si T(1) and T(2) NMR relaxation in porous paramagnetic material SiO(2)-MnO-Al(2)O(3)

The (29)Si spin-lattice relaxation in porous silica-based material 1, doped by ions Mn(2+) at a Si/Mn ratio of 3.5, is non-exponential, independent of magic-angle spinning (MAS) rates and governed by direct dipolar coupling between electron and nucleus where an electron relaxation time is estimated to be about 10(-8)s. In the absence of mutual energy-conserving spin flips (spin diffusion) in 1, the (29)Si T(2) time increases linearly with spinning rates. None was observed in diamagnetic porous system 2. The unexpected (29)Si T(2) dependence has been interpreted in terms of the large bulk magnetic susceptibility (BMS) effects. It has been shown that editing the (29)Si Hahn-echo MAS NMR spectra eliminates wide lines, belonging to (29)Si nuclei in the proximity of paramagnetic centers, and reduces the BMS broadenings in sideband patterns for nuclei remote from these centers.     

Magnetoelectric effects in multiferroic Y-type hexaferrites Ba_(0.3)Sr_(1.7)Co_xMg_(2-x)Fe_(12)O_(22)

Y-type hexaferrites with tunable conical magnetic structures are promising single-phase multiferroics that exhibit large magnetoelectric effects. We have investigated the influence of Co substitution on the magnetoelectric properties in the Y-type hexaferrites Ba(0.3)Sr(1.7)CoxMg(2-x)Fe(12)O(22)(x = 0.0, 0.4, 1.0, 1.6). The spin-induced electric polarization can be reversed by applying a low magnetic field for all the samples. The magnetoelectric phase diagrams of BaBa(0.3)Sr(1.7)CoxMg(2-x)Fe(12)O(22) are obtained based on the measurements of magnetic field dependence of dielectric constant at selected temperatures. It is found that the substitution of Co ions can preserve the ferroelectric phase up to a higher temperature, and thus is beneficial for achieving single-phase multiferroics at room temperature.     

Torsional Splitting in the nu(5) Fundamental Infrared Band of CH(3)CD(3) and (13)CH(3)CD(3)

The nu(5) fundamental (C-C stretching) of CH(3)CD(3) shows a resolved torsional structure, caused by perturbations due mainly to the linear dependence of the torsional potential barrier on the normal coordinate Q(5). We were able to analyze this structure and to assign vibration-rotation transition wavenumbers for all five torsional components, classified according to the symmetry species of the G(18)((3)) extended molecular group. The torsional splitting pattern is qualitatively similar to that of a nondegenerate vibrational state with an even number of excited torsional quanta v(6). Explorative calculations show that the main perturber system should consist of the torsional components of the vibrational ground state correlating with v(6)=4 in the high barrier limit. The strength of the perturbation on the E(r0) torsional components of nu(5) increases rapidly with r, the E(40) component being the most affected. The observed transition wavenumbers can be reasonably fitted by a simplified model containing independent effective vibration-rotation parameters for the five different torsional components of nu(5), for both CH(3)CD(3) and (13)CH(3)CD(3). The trend of the determined values of the effective vibrational wavenumbers and rotational parameters over the torsional components supports the proposed vibration-torsion interaction mechanism, responsible for the observed torsional splittings. A strong anomaly observed in the rotational intensity distribution of nu(5) is discussed. Copyright 2001 Academic Press.     

Magnetic glass in shape memory alloy: Ni(45)Co(5)Mn(38)Sn(12)

The first order martensitic transition in the ferromagnetic shape memory alloy Ni(45)Co(5)Mn(38)Sn(12) is also a magnetic transition and has a large field induced effect. While cooling in the presence of a field this first order magnetic martensite transition is kinetically arrested. Depending on the cooling field, a fraction of the arrested ferromagnetic austenite phase persists down to the lowest temperature as a magnetic glassy state, similar to the one observed in various intermetallic alloys and in half doped manganites. A detailed investigation of this first order ferromagnetic austenite (FM-A) to low magnetization martensite (LM-M) state transition as a function of temperature and field has been carried out by magnetization measurements. Extensive cooling and heating in unequal field (CHUF) measurements and a novel field cooled protocol for isothermal MH measurements (FC-MH) are utilized to investigate the glass like arrested states and show a reverse martensite transition. Finally, we determine a field-temperature (HT) phase diagram of Ni(45)Co(5)Mn(38)Sn(12) from various magnetization measurements which brings out the regions where thermodynamic and metastable states coexist in the HT space, clearly depicting this system as a 'magnetic glass'.     

Recording of second-harmonic index gratings in photorefractive (K(0.5) Na(0.5))(0.2) (Sr(0.75) Ba(0.25))(0.9) Nb(2)O(6) crystals

We propose and demonstrate a novel method for recording second-harmonic volume index gratings in photorefractive crystals. The fundamental component of the index grating is eliminated by means of a pi -phase shifted double-exposure process that uses the Mach-Zehnder interferometric technique. Experimental results for (K(0.5) Na(0.5)) (0.2)(Sr> (0.75)Ba (0.25))(0.9)Nb (2)O(6) crystals are presented and discussed.     

Multiple magnetic transitions in single crystals of Ce_(12)Fe_(57.5)As_(41) and La_(12)Fe_(57.5)As_(41)

Measurements of magnetic and transport properties were performed on needle-shaped single crystals of Ce_(12)Fe_(57.5)As_(41)and La_(12)Fe_(57.5)As_(41).The availability of a complete set of data enabled a side-by-side comparison between these two rare earth compounds.Both compounds exhibited multiple magnetic orders within 2-300 K and metamagnetic transitions at various fields.Ferromagnetic transitions with Curie temperatures of 100 and 125 K were found for Ce_(12)Fe_(57.5)As_(41)and La_(12)Fe_(57.5)As_(41),respectively,followed by antiferromagnetic type spin reorientations near Curie temperatures.The magnetic properties underwent complex evolution in the magnetic field for both compounds.An antiferromagnetic phase transition at about 60 K and 0.2 T was observed merely for Ce_(12)Fe_(57.5)As_(41).The field-induced magnetic phase transition occurred from antiferromagnetic to ferromagnetic structure.A strong magnetocrystalline anisotropy was evident from magnetization measurements of Ce_(12)Fe_(57.5)As_(41).A temperature-field phase diagram was present for these two rare earth systems.In addition,a logarithmic temperature dependence of electrical resistivity was observed in the two compounds within a large temperature range of 150-300 K,which is rarely found in 3D-based compounds.It may be related to Kondo scattering described by independent localized Fe 3d moments interacting with conduction electrons.     

Novel dielectric anomaly in the hole-doped La(2)Cu(1-x)Li(x)O(4) and La(2-x)Sr(x)NiO(4) insulators: signature of an electronic glassy state

The low-frequency dielectric response of hole-doped insulators La(2)Cu(1-x)Li(x)O(4) and La(2-x)Sr(x)NiO(4) shows a large dielectric constant epsilon(') at high temperature and a steplike drop by a factor of 100 at a material-dependent low temperature T(f). T(f) increases with frequency, and the dielectric response shows universal scaling in a Cole-Cole plot, suggesting that a charge-glass state is realized both in the cuprates and in the nickelates.     

Quasiparticles in the superconducting state of Bi(2)Sr(2)CaCu(2)O(8+delta)

Recent improvements in momentum resolution lead to qualitatively new angle-resolved photoemission spectroscopy results on the spectra of Bi(2)Sr(2)CaCu(2)O(8+delta) (Bi2212) along the (pi,pi) direction, where there is a node in the superconducting gap. We now see the intrinsic line shape, which indicates the presence of true quasiparticles at all Fermi momenta in the superconducting state, and lack thereof in the normal state. The region of momentum space probed here is relevant for charge transport, motivating a comparison of our results to conductivity measurements by infrared reflectivity.     

Stability of (3)He(2)(4)He(n) and (3)He(3)(4)He(n) L=0 clusters

We have studied the stability of mixed (3)He/(4)He clusters in L=0 states by the diffusion Monte Carlo method, employing the Tang-Toennies-Yiu He-He potential. The clusters (3)He(4)He(N) and (3)He(2)(4)He(N) are stable for N>1. The lighter atoms tend to move to the surface of the cluster. The minimum number of 4He atoms able to bind three 3He atoms in a L=0 state is nine. Two of three fermionic helium atoms stay on the surface, while the third one penetrates into the cluster.     

The Comet-Tail (A(2)Pi(i)-X(2)Sigma(+)) System of (12)C(16)O(+): A Reinvestigation

The emission spectrum of the comet-tail (A(2)Pi(i)-X(2)Sigma(+)) system of (12)C(16)O(+) produced in the cathode glow of a hollow-cathode discharge tube and photographed in the spectral region 3345-8500 ? at high resolution was reinvestigated. Detailed rotational analysis of 10 bands involving 5 vibrational levels v = 0 to 4 of each of the A and X states was carried out. Spin-splitting of the rotational levels was observed for the analyzed bands. The observed intensity distribution of the branches is found to be in good agreement with theoretical calculations. Molecular constants for both the A and X states were obtained from a global fit of the present data of the A-X system and the infrared and microwave data available from the literature for v = 0, 1, 2, 3, and 4 of state X, using effective Hamiltonian for the A(2)Pi state and matrix elements for both A and X states. The present work suggests that the A(2)Pi(i) state changes from Hund's case (a) at low J values to Hund's case (b) at high J values. Copyright 2000 Academic Press.     

Metastability and inverse magnetocaloric effect in doped manganite (Nd(0.25)Sm(0.25)Sr(0.5)MnO(3)) and ferromagnetic shape memory alloy (Ni(2)Mn(1.36)Sn(0.64)): a comparison

The manganite Nd(0.25)Sm(0.25)Sr(0.5)MnO(3) (NSSMO) shows a first-order metal to insulator transition on cooling, which is concomitant with a magnetic transition from the ferromagnetic to antiferromagnetic state. In some respect the sample shows a striking similarity with Ni-Mn-Sn based ferromagnetic shape memory alloys (FSMAs) undergoing a first-order magneto-structural transition, and efforts have been made to highlight the similarities and dissimilarities of the studied manganite with one such FSMA of composition Ni(2)Mn(1.36)Sn(0.64). From our transport and magnetic investigations, the region of transition in the NSSMO is found to be highly metastable, with a clear indication of a magnetically arrested state which persists even when the sample is cooled down to the lowest temperature of measurement. Interestingly, the studied manganite shows an inverse magnetocaloric effect similar to the FSMA. However, a striking difference between the two compositions is evident in the low-temperature magneto-transport behavior: while a clear signature of tunneling magnetoresistance is present in NSSMO due to the coexisting metallic and insulating clusters of nanometer dimension, the studied FSMA do not show such behavior due to the absence of any insulating phase in the intermetallic alloy.     

Theoretical Study of the Collision-Induced Double Transition CO(2) (nu(3) = 1) + N(2) (nu(1) = 1) <-- CO(2) (nu(3) = 0) + N(2) (nu(1) = 0) at 296 K

A procedure is presented for the calculation of the double vibrational collision-induced absorption CO(2) (nu(3) = 1) + N(2) (nu(1) = 1) <-- CO(2) (nu(3) = 0) + N(2) (nu(1) = 0) on the basis of quantum lineshapes computed using an isotropic potential and dipole-induced dipole functions. The linestrengths and energies of the vibration-rotation transitions are treated explicitly for N(2), utilizing the HITRAN database for CO(2). The theoretical absorption profile is compared to recent experimental results. By narrowing the width of the individual lines contributing to the overall absorption profile relative to their values determined for N(2)-N(2) collision-induced absorption, excellent agreement between theory and experiment is obtained. Copyright 2000 Academic Press.     

Efficient measurement of (3)J(N,Cgamma) and (3)J(C',Cgamma) coupling constants of aromatic residues in (13)C, (15)N-labeled proteins

An NMR pulse sequence is proposed for the simultaneous determination of side chain chi1 torsion-angle related (3)J(N,Cgamma) and (3)J(C', Cgamma) couplings in aromatic amino acid spin systems. The method is of the quantitative J correlation type and takes advantage of attenuated (15)N and (1)H transverse relaxation by means of the TROSY principle. Unlike previously developed schemes for the measurement of either of the two coupling types, spectra contain internal reference peaks that are usually recorded in separate experiments. Therefore, the desired information is extracted from a single rather than four data sets. The new method is demonstrated with uniformly (13)C/(15)N labeled Desulfovibrio vulgaris flavodoxin, which contains 14 aromatic out of 147 total amino acid residues.     

Second-harmonic generation in quasi-periodically domain-inverted Sr(0.6) Ba(0.4) Nb(2)O(6) optical superlattices

One-dimensional Fibonacci-type quasi-periodically domain-inverted structures have been successfully fabricated in a strontium barium niobate crystal by electric field poling. With a single such structure, type I phase-matched second-harmonic generation (SHG) has been demonstrated at several wavelengths from red to near ultraviolet. The spectral positions of the observed SHG peaks are in good agreement with theoretical predictions. The range of measured conversion efficiencies is 2-10%.     

Signatures of a hybridization gap in magnetic susceptibility of Ce(1-x)La(x)Os(4)Sb(12)

The magnetic susceptibility of Ce(1-x)La(x)Os(4)Sb(12), with x ≈ 0.2, exhibits a pronounced maximum at T(m) = 80 K. This T(m) coincides roughly with the temperature below which a small gap, believed to be a hybridization gap, is observed in spectroscopic measurements in undoped CeOs(4)Sb(12). However, a similar anomaly, at a lower temperature of 50 K, is observed in LaOs(4)Sb(12). Furthermore, there is a monotonic variation of T(m) with x, for x > 0.2, suggesting the same origin of the two anomalies and undermining a simple hybridization gap interpretation of the susceptibility of Ce(1-x)La(x)Os(4)Sb(12) alloys, with x < 1. A possibility of the hybridization gap opening, induced by freezing out of local phonons, strongly coupled with electronic degrees of freedom, is discussed.     

Quantum diffusion in polaron model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers

We numerically investigate quantum diffusion of an electron in a model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers with fluctuation of the parameters due to the impact of colored noise. The randomness is introduced by fluctuations of distance between two consecutive bases along the stacked base pairs. We demonstrate that in the model the decay time of the correlation can control the spread of the electronic wavepacket. Furthermore it is shown that in a motional narrowing regime the averaging over fluctuation causes ballistic propagation of the wavepacket, and in the adiabatic regime the electronic states are affected by localization.     

Magnetic properties of (Co Pd ) superstructures on Pd(100) and Pd(111)

The magnetic properties of (Co_nPd_m)_r superstructures on Pd(100) and Pd(111) are evaluated using the fully-relativistic spin-polarized screened Korringa-Kohn-Rostoker method. It is found that only in the case of a Pd(111) substrate such superstructures exhibit perpendicular magnetism, while on a Pd(100) substrate the magnetization is oriented in-plane. Also investigated is the effect of interdiffusion in repeated superstructures. By using the inhomogeneous coherent potential approximation (CPA) for layered systems the effect of ordering into (repeated) superstructures can be described in an ab-initio-like manner. It is found that already small amounts of interdiffusion can be decisive for the actual value of the magnetic anisotropy energy. Received 3 November 1999 and Received in final form 18 January 2000