Interplay between mesoscopic phase separation and bulk magnetism in the layered NaxCoO2

Specific heat of the layered NaxCoO2 (x=0.65, 0.70 and 0.75) oxides has been measured in the temperature range of 3-360 K and magnetic field of 0 and 9 T. The analysis of data, assuming the combined effect of inter-layer superexchange and the phase separation into mesoscopic magnetic domains with localized spins embedded in a matrix with itinerant electronic character, suggests that the dominant contribution to the specific heat in the region of short-range ordering is mediated by quasi-2D antiferromagnetic clusters, perpendicular to the CoO2 layers

Orbital non-Fermi-liquid behavior in cubic ruthenates

We peruse various anomalous physical responses of the cubic (ferromagnetic SrRuO3 and paramagnetic CaRuO3) ruthenates, such as fractional power-law conductivity, anomalous Raman line shapes, and Hall currents. We show how these exciting power-law observations are naturally described within a new, local (orbital) non-Fermi-liquid state arising from strong, multiorbital Coulomb interactions. Introducing a multiorbital, correlated model treated within the dynamical mean-field theory, we also find two distinct relaxation rates for relaxation of transport in complete agreement with experiment

Charge transfer mechanism and Tc(x) dependence in Y0.8(Ca)0.2Ba2Cu3O6+x

We propose a model for charge transfer mechanism in Y0.8(Ca)0.2Ba2Cu3O6+x to count hole doping of CuO2 planes and x dependence of critical transition temperature T_c. It is assumed the total number of doped holes in the planes is sum of holes that are introduced through two separate channels: substitution of Y3+ by Ca2+ and from CuO chains that are longer than a minimal (critical) length l_min needed for charge transfer to take place. The T_c(x) dependence is obtained by combining calculated x dependence of doping, p(x), and universal T_c versus p relation. Although calculated T_c(x) dependences for l_min=3 and l_min=4 both remarkably correlate to the experimental T_c(x), we argue that the value l_min=4 gives a reasonable overall agreement.Comment: Four pages of text, 2 figures, corrected typing error in abstract: Y2+ and Ca3+ replaced by Y3+ and Ca2+. Thw word "each" added in page 3, line 4. Accepted in Superconductor Science and Technology, on 07.Apr.2008, after having been considerably revise

Magnetic studies of Ca1-xMxRuO3 (M=La and Sr)

CaRuO3 is a perovskite with an orthorhombic distortion and shows the characteristics of spin-glass behavior below TC=87 K. The La3+ substitution for Ca2+ in Ca1-xLaxRuO3 samples, induces a disorder in the Ca site (the A site) and the system becomes antiferromagnetically (AFM) ordered with TN = 58 and 19 K for x=0.1 x=0.5 respectively. In the Ca1-xSrxRuO3 system, the Ca0.8Sr0.2RuO3 sample is canted-AFM ordered at 107 K. The compounds with higher Sr concentration display ferromagnetic behavior and the saturation moment increases with Sr. Huge magnetic hysteresis loops are obtained at low temperatures. The coercive field (HC) decreases with Sr. For x=0.4 HC =9.5 kOe (at 5 K) whereas for SrRuO3 HC =2.4 kOe. For x=0.4 and 0.6, HC decreases sharply with temperature and than increases again with a peak at 95 and 115 K, respectively. On the other hand, for SrRuO3, HC remains practically unchanged up to 50 K and shows a peak at 90 K and than decrease sharply up to TC =165 K.Comment: This paper was submitted to JMM

On Blind Identifiability of FIR-MIMO Systems with Cyclostationary Inputs Using Second Order Statistics

We consider a general nn MIMO system excited by unobservable inputs that are spatially independent, cyclostationary with unknown statistics. Such a MIMO scenario appears in many applications, such as multi-user communications and separation of competing speakers in speech processing. A special case of this problem, i.e., a 22 system case, was recently addressed in [1] using frequency-domain correlations of the system output. In this paper we provide a set of conditions under which a general n n system is uniquely identifiable based on the second-order frequency-domain correlations of the system output. We provide a constructive proof for the uniqueness of the system solution, which could also serve as a basis for a practical algorithm for system identification

Blind MIMO FIR Channel Identification Based on Second-Order Spectra Correlations

We consider a problem of identifying a Multiple-Input Multiple-Output (MIMO) finite impulse response system excited by colored inputs with known statistics. We propose a new, nonlinear optimization based method that involves the power spectra and cross-spectra of the system output. The proposed algorithm is tested for the case of cyclostationary inputs (CDMA scenario) and stationary inputs (SDMA scenario). Simulation results indicate that the proposed scheme works well, even for large order systems, and is robust to noise and channel length mismatch

Blind Equalization Of Multiuser CDMA Channels: A Frequency-Domain Approach

We address the problem of blind equalization of mixing channels, resulting from frequency selective fading and multipath in a multi-user CDMA system. We present a novel frequency-domain approach that employs second order spectral statistics of the observations and the users signatures. Unlike other methods, which are based on time-domain analysis, no particular assumptions are made about the support of the mixing channels, except that they have finite length. Since signatures correlations, rather that signatures themselves, are used, the proposed estimation is independent of users delays. Although performance does depend on the users signatures, signatures orthogonality is not required. 1. INTRODUCTION Code Division Multiple Access (CDMA) communication systems have attracted a lot of attention recently due to their efficient utilization of the available bandwidth and their flexibility in accommodating variable traffic patterns. In CDMA each user is assigned a unique code sequence, whi..