arXiv subjects

Sher Alam

Publications and source records attributed to Sher Alam.

At least 19 recordsLinked to original sources

arXiv2017

Constraining capability of $Z γh$ production at the ILC

Higgs boson couplings with gauge bosons are probed through $e^-e^+ \rightarrow Z γh$ in an effective Lagrangian framework. For this study the beam polarization facility at the ILC along with the typical center-of-mass energy of 500 GeV is considered. The reach of the ILC with an integrated luminosity of 300 fb$^{-1}$ in the determination of $CP$-conserving parameters is obtained. Sensitivity of the probe of each of these couplings in the presence of other couplings is investigated. The most influential coupling parameters are $\bar c_W=-\bar c_B$. Other parameters of significant effect are $\bar c_{HW}$ and $\bar c_{HB}$. A detailed study of the various kinematic distributions represents possibilities to disentangle the effect of some of these couplings.

hep-ph↗

arXiv2006

Heat Capacity study of $β$-FeSi$_2$ single crystals

Heat Capacity of needle-like [length=5mm, diameter=1 mm] $β$-FeSi$_{2}$ single crystal, grown by chemical vapor transport has been measured. Two anomalies are found, a broad deviation centered around 160 K and a clear deviation at a temperature of 255 K approximately. We have attempted to relate these to the anomalies previously reported in the case of the resistivity data. The Transient Thermoelectric Effect [TTE] results lead us to the inference that the system under goes from single carrier system to at least two carrier system at 220 K-our heat capacity results seem to provide further independent evidence for this transition in this system.

cond-mat.mtrl-sci↗

arXiv2005

Clear Experimental Signature of Charge-Orbital density wave in Nd$_{1-x}$Ca$_{1+x}$MnO$_{4}$

Single Crystals of Nd$_{1-x}$Ca$_{1+x}$MnO$_{4}$ have been prepared by the travelling floating-zone method, and possible evidence of a charge -orbital density wave in this material presented earlier [PRB68,092405 (2003)] using High Resolution Electron Microscopy [HRTEM] and Electron Diffraction [ED]. In the current note we present direct evidence of charge-orbital ordering in this material using heat capacity measurements. Our heat capacity measurements indicate a clear transition consistent with prior observation. We find two main transitions, one at temperature $T_{_H}=310-314$ K, and other at $T_{_A}=143$ K. In addition, we may also conclude that there is a strong electron-phonon coupling in this material.

cond-mat.str-el↗

arXiv2005

Local Electronic Structure of PbVO3, a New Member of PbTiO3 Family, studied by XANES/ELNES

Recently an interesting multi-ferroic system PbVO3 [Chem. Mater. 2004] was successfully prepared using a high-pressure and high-temperature technique. The crystallographic features were reported. In this note we concentrate on the theoretical XANES spectra by considering the K-edge of Vanadium. The tetragonality [c/a=1.229 at 300 K] of PbVO3 is the largest in the PbTiO3 family of compounds. Thus one is led naturally to examine the effect of the change of tetragonality and the axial oxygen position on the electronic structure [i.e. XANES spectrum]. We study this effect in two ways. At a given temperature we vary the tetragonality and the axial oxygen position and quantify it in terms of XANES difference spectrum. Secondly, we compute the XANES spectra at three different temperatures, 90 K, 300 K, and 530 K and quantify the change in terms of the difference spectrum. We note that in this compound the tetragonality increases almost monotonically with temperature from 12 K to 570 K without transition to the cubic phase under ambient pressure. A key objective of the current investigation is to gain an understanding of various absorption features in the vicinity of K-edge of V, in terms of valence, local site symmetry, local coordination geometry, local bond distances, charge transfer, and local projected density of states. We consider both the polarized and the unpolarized XANES spectra. In short we have performed a local electronic study, which nicely complements the crystallographic features reported recently in PbVO3.

cond-mat.mtrl-sci↗

arXiv2004

X-ray Absorption Near Edge Structure of FePt nanoclusters

X-ray Absorption Near Edge Structure [XANES] of FePt nanoclusters has been studied using a full multiple scattering, self-consistent field [SCF], real-space Green`s function approach realized via the powerful ab initio FEFF8 code. One purpose of our study is to determine the sensitivity of Pt L3 edge with respect to the size and shape of the FePt nanoclusters. We also give the results of the calculations with respect to the Fe L3 edge. Calculations are made with and without core-hole for two main reasons, to check and cross-check the FEFF code and also since in some cases it is known such as Pt clusters that better results are obtained without the core-hole. This is mainly because the screening electron will occupy empty d or f states and correspondingly reduce the white line intensity.

cond-mat.mtrl-sci↗

arXiv2002

Quantum Group Based Theory for Antiferromagnetism and Superconductivity: Proof and Further Evidence

Previously one of us presented a conjecture [APF-4 Proceedings] to model antiferromagnetism and high temperature superconductivity and their 'unification' by quantum group symmetry rather than the corresponding classical symmetry in view of the critique by Baskaran and Anderson of Zhang's classical SO(5) model. This conjecture was further sharpened, experimental evidence and the important role of 1-d systems [stripes] was emphasized and moreover the relationship between quantum groups and strings via WZWN models were given in [Phys. Lett A272, (2000)]. In this brief note we give and discuss mathematical proof of this conjecture, which completes an important part of this idea, since previously an explicit simple mathematical proof was lacking. Moreover an independent calculation [IC/99/2] which constructs the generators forming SO(5) algebra not only supports our previous conjecture but provides a check on our calculations. It is important to note that in terms of physics that the arbitariness [freedom] of the d-wave factor g$^{2}$(k) is tied to quantum group symmetry whereas in order to recover classical SO(5) one must set it to unity in an adhoc manner. We intuitively expect that this freedom may be related to psuedogap behaviour in cuprates.

cond-mat.supr-con↗

arXiv2002

Temperature Dependent Polarized XANES Spectra for Zn-doped LSCO system

The cuprates seem to exhibit statistics, dimensionality and phase transitions in novel ways. The nature of excitations [i.e. quasiparticle or collective], spin-charge separation, stripes [static and dynamics], inhomogeneities, psuedogap, effect of impurity dopings [e.g. Zn, Ni] and any other phenomenon in these materials must be consistently understood. Zn-doped LSCO single crystal were grown by TSFZ technique. Temperature dependent Polarized XANES [near edge local structure] spectra were measured at the BL13-B1 [Photon Factory] in the Flourescence mode from 10 K to 300 K. Since both stripes and nonmagnetic Zn impurities substituted for Cu give rise to inhomogeneous charge and spin distribution it is interesting to understand the interplay of Zn impurities and stripes. To understand these points we have used Zn-doping and some of the results obtained are as follows: The spectra show a strong dependence with respect to the polarization angle, $θ$, as is evident at any temperature by comparing the spectra where the electric field vector is parallel with ab-plane to the one where it is parallel to the c-axis. By using the XANES [temperature] difference spectra we have determined T* [experimentally we find, T* $\approx$ 160-170 K] for this sample. The XANES difference spectra shows that the changes in XANES features are larger in the ab-plane than the c-axis, this trend is expected since zinc is doped in the ab-plane at the copper site. Our study also complements the results in literature namely that zinc doping does not affect the c-axis transport.

cond-mat.supr-con↗

arXiv2001

Quantum Groups, Strings and HTSC materials II

Previously we have indicated the relationship between quantum groups [Phys. Lett A272, (2000)] and strings via WZWN models in the context of applications to cuprates and related materials.The connection between quantum groups and strings is one way of seeing the validity of our previous conjecture [i.e. that a theory for cuprates may be constructed on the basis of quantum groups]. The cuprates seems to exhibit statistics, dimensionality and phase transitions in novel ways. The nature of excitations [i.e. quasiparticle or collective] must be understood. The Hubbard model captures some of the behaviour of the phase transitions in these materials. On the other hand the phases such as stripes in these materials bear relationship to quantum group or string-like solutions. One thus expects that the relevant solutions of Hubbard model may thus be written in terms of stringy solutions. In short this approach may lead to the non-perturbative formualtion of Hubbard and other condensed matter Hamiltonians. The question arises that how a 1-d based symmetry such as quantum groups can be relevant in describing a 3-d [spatial dimensions] system such as cuprates. The answer lies in the key observation that strings which are 1-d objects can be used to describe physics in $d$ dimensions. For example gravity [which is a 3-d [spatial] plus time] phenomenon can be understood in terms of 1-d strings. Thus we expect that 1-d quantum group object induces physics in 2-d and 3-d which may be relevant to the cuprates. We present support for our contention using [numerical] variational Monte-Carlo [MC] applied to 2d d-p model. We also briefly discuss others ways to formulate a string picture for cuprates, namely by exploiting connection between gauge theories and strings and t'Hooft picture of quark confinement.

cond-mat.supr-con↗

arXiv2001

EXAFS study of Tl$_{0.75}$Cu$_{.25}$Ba$_2$Ca$_3$Cu$_4$ O$_y$ and Cu$_{0.68}$C$_{.32}$Ba$_2$Ca$_3$Cu$_4$ O$_y$ superconductors [bulk] at 300 K

The results of EXAFS measurements at 300 K for the superconducting compounds Tl$_{0.75}$Cu$_{0.25}$Ba$_{2}$Ca$_{3}$Cu$_4$O$_{y}$ [Tl-1234], TlBa$_{2}$Ca$_{3}$Cu$_{4}$O$_{y}$ [Tl-1212], and CuBa$_{2}$Ca$_{3}$Cu$_{4}$O$_{y}$ [Cu-1234]. are reported. We have measured the EXAFS spectrum for Tl$_{0.75}$Cu$_{0.25}$Ba$_{2}$Ca$_{3}$Cu$_4$O$_{y}$ in the range 10K-300K, however here we limit our discussion to the spectrum at 300 K. This material is prepared under high pressure [3.5 GPa] from precursors with small carbon concentrations and exhibits a T$_c$ of $~127$ K. We have also performed ``aging'' study by looking at XRD for this material after approximately one year. The XRD results at 300 K are ``unchanged''. It is of interest to compare the EXAFS spectrum of this compound with the corresponding compound Cu-1234. Remarks on the choice of appropriate EXAFS standard for this and related compounds are also given. Based on our data analysis we quantify disorder in these systems. By using the Cu-O in-plane distance we give values for the microstrain parameter, which can be related to the charge ordering transition.

cond-mat.supr-con↗

arXiv2001

SET based experiments for HTSC materials: II

The cuprates seem to exhibit statistics, dimensionality and phase transitions in novel ways. The nature of excitations [i.e. quasiparticle or collective], spin-charge separation, stripes [static and dynamics], inhomogeneities, psuedogap, effect of impurity dopings [e.g. Zn, Ni] and any other phenomenon in these materials must be consistently understood. In this note we further discuss our original suggestion of using Single Electron Tunneling Transistor [SET] based experiments to understand the role of charge dynamics in these systems. Assuming that SET operates as an efficient charge detection system we can expect to understand the underlying physics of charge transport and charge fluctuations in these materials for a range of doping. Experiments such as these can be classed in a general sense as mesoscopic and nano characterization of cuprates and related materials. In principle such experiments can show if electron is fractionalized in cuprates as indicated by ARPES data. In contrast to flux trapping experiments SET based experiments are more direct in providing evidence about spin-charge separation. In addition a detailed picture of nano charge dynamics in cuprates may be obtained.

cond-mat.supr-con↗

arXiv2001

Parameters for Systems Exhibiting Local Lattice Distortions, Charge and Spin Ordering

Keeping in mind the experimental results that indicate local lattice distortions, charge and spin orderings, we have developed a phenomenological approach which allows us to describe the electronic phase diagram of cuprates and related systems in terms of few parameters.In the present work we consider a third-order parameter theory which characterize charge, spin and superconductivity orderings. We are thus led to a theory of three scalar fields. By coupling these scalars to gauge fields we are naturally led to string-like solutions, which we interpret as stripes. This ties nicely with our quantum group conjecture that 1d systems play an important role in the physics of cuprates and related materials. We show that this simple approach can give rough values for two-order parameters which can be naively be interpreted as charge and spin orderings. We also report our attempt to understand how local lattice distortions are involved and what role they play in terms of these two order parameters.

cond-mat.supr-con↗

arXiv2001

Quantum Group based Modeling for the description of high temperature superconductivity and antiferromagnetism: Some supporting evidence

Following our recent conjecture to model the phenomenona of antiferromagnetism and superconductivity by quantum symmetry groups, we propose in the present note three toy models, namely, one based on SO_{q}(3) the other two constructed with the SO_{q}(4) and SO_{q}(5) quantum groups. Possible motivations and rationale for these choices are outlined. One of the prime motivations underlying our proposal is the experimental observation of stripe structure [phase] in high T_c superconductivity [HTSC] materials. A number of experimental techniques have recently observed that the CuO_{2} are rather inhomogeneous, providing evidence for phase separation into a two component system. i.e. carrier-rich and carrier-poor regions. In particular, extended x-ray absorption fine structure [EXAFS] demonstrated that these domains forms stripes of undistorted and distorted local structures alternating with mesoscopic length scale comparable with coherence length in HTSC. Evidence for our conjecture is discussed.

cond-mat↗

arXiv2001

Quantum Groups, Strings and HTSC materials

Previously we have indicated the relationship between quantum groups and strings via WZWN models. In this note we discuss this relationship further and point out its possible applications to cuprates and related materials. The connection between quantum groups and strings is one way of seeing the validity of our previous conjecture [i.e. that a theory for cuprates may be constructed on the basis of quantum groups]. The cuprates seems to exhibit statistics, dimensionality and phase transitions in novel ways. The nature of excitations [i.e. quasiparticle or collective] must be understood. The Hubbard model captures some of the behaviour of the phase transitions in these materials. On the other hand the phases such as stripes in these materials bear relationship to quantum group or string-like solutions. One thus expects that the relevant solutions of Hubbard model may thus be written in terms of stringy solutions. In short this approach may lead to the non-perturbative formualtion of Hubbard and other condensed matter Hamiltonians. The question arises that how a 1-d based symmetry such as quantum groups can be relevant in describing a 3-d [spatial dimensions] system such as cuprates. The answer lies in the key observation that strings which are 1-d objects can be used to describe physics in $d$ dimensions. For example gravity [which is a 3-d [spatial] plus time] phenomenon can be understood in terms of 1-d strings. Thus we expect that 1-d quantum group object induces physics in 2-d and 3-d which may be relevant to the cuprates.

cond-mat.supr-con↗

arXiv2000

SET based experiments for HTSC materials

cond-mat.supr-con↗

arXiv2000

One-loop sfermion corrections to $e^-e^+ \to W^-W^+$ in the MSSM

We study one-loop effects of sfermions on helicity amplitudes for $\eeww$ in the Minimal Supersymmetric Standard Model. The one-loop contributions are calculated in the $\bar{\rm MS}$ renormalization scheme. In order to verify the validity of the analytic calculation and the numerical program, the following tests are performed. (i) The BRS sum rules hold exactly among the analytic expressions of the form factors of the $\eeww$ amplitude and those of the amplitudes where the external $W^\pm$ bosons are replaced by the corresponding Goldstone bosons $χ^\pm$, hence they hold within the expected accuracy of the numerical program. (ii) The one-loop sfermion contribution to the amplitudes decouple in the heavy mass limit. This property is used to test the overall normalization of the amplitudes. In order to observe the analytically exact decoupling, the amplitudes are expanded by the $\bar{\rm MS}$ couplings of the Standard Model. (iii) The high-energy analytic formulas of the helicity amplitudes, which are verified by using the equivalence theorem analytically, are used for the numerical test of the high energy behavior of the amplitudes. We then investigate the magnitude of the one-loop effects on each helicity amplitude which may be measured by experiments at future linear colliders. Under the constraint from available precision data, the one-loop corrections to a few helicity amplitudes (for example, the longitudinal-$W$-pair production) can be at most from -0.8% to $+0.6$% in magnitude in the observables. The corrections in the helicity-summed cross sections are smaller, typically a few times $\pm 0.1$% at large scattering angles.

hep-ph↗

arXiv2000

Quantum group conjecture and Stripes

Keeping in mind our conjecture of modelling cuprates and related systems by quantum groups and our claim that the existence of stripes is intimately related to quantum groups and more strongly is a consequence of the underlying quantum group structure we note that a recent claim that {\em magnetic fluctuations} also displays a one-dimensional character makes our conjecture more viable. The recent strong claim by Mook et al., if true further supports our intuition. For the fluctuations associated with a striped phase are expected to be one-dimensional, whereas the magnetic fluctuations are {\em taken} to display two-dimensional symmetry. It is claimed by Mook et al. that this apparent two-dimensionality results from measurements on twinned crystals, and that similar measurements on substantial detwinned crystals of YBa$_{2}$Cu$_{3}$O$_{6.6}$ reveal the one-dimensional character of the magnetic fluctuations thus making the stripe scenario more stronger, in other words there are also magnetic stripes. As noted before in our conjecture that one of the main reason for quantum groups to model cuprates is that they are directly related to the symmetries of one-dimensional systems. Thus now if the magnetic fluctuations are also shown exhibiting one-dimensional behavior that all the more {\em directly strengthens our conjecture}. However we note that our conjecture is more generic and not tied to the one-dimensional character of the now claimed magnetic fluctuations. Simply the one-dimesional nature of magnetic fluctuations as noted by Mook et al., makes our conjecture more {\em obvious} and clearer.

cond-mat.supr-con↗

arXiv2000

The patching of critical points using quantum group

Following our recent conjecture to model the phenomenona of antiferromagnetism and superconductivity by quantum symmetry groups, we discuss in the present note how to construct a workable scenario using this symmetry. In particular we propose to patch the relevant critical points. This means we identify fixed points, corresponding to various $k$ or $q$ [since the two are related] and make expansion around these points, to control these expansion we can impose gauge structure and we thus arrive at quantum group based gauge theory or collection of classical gauge theories which represent the condensed matter system such as cuprates. This is different than ordinary gauge theories in several ways, for in ordinary field theory one has well-defined critical point here the critical points are not unique or simple. In short the real transition than in condensed matter system is represented by collection or {\it ensemble average} of the several chosen critical points which come from ordinary field theory [gauge theory]. This idea may reveal the connection between Hubbard model and gauge theory and string theory. In short it can lead to the non-perturbative formualtion of Hubbard and other condensed matter Hamiltonians.

cond-mat.supr-con↗

arXiv2000

The choice of the symmetry group for the cuprates

Following our recent conjecture to model the phenomenona of antiferromagnetism and superconductivity by quantum symmetry groups, we discuss in the present note the choice of the classical symmetry group underlying the quantum group. Keeping in mind the degrees of freedom arising from spin, charge, and lattice we choose the classical group as SO(7). This choice is also motivated to accomodate the several competing phases which are or may be present in these and related materials, such as stripe phase [mesoscopically ordered phase], Luttinger liquids, nearly antiferromagnetic Fermi liquids, charge-ordered Fermi liquids, glassy phase, stringy phase and perhaps more. The existence and the behavior of pseudo-gap and lattice distortion are also an important consideration. We have lumped the charge, spin and lattice-distortion ordering and other orderings into the psuedogap.

cond-mat.supr-con↗