Considerations on the symmetry of loop order in cuprates and some effects accompanying it (2009)
The loop-current state discovered in the pseudogap phase of cuprates breaks time reversal symmetry and lowers the point group symmetry of the crystal. The order parameter and the magnetic structure...
Magnetically tunable dielectric materials (2009)
Lawes, G., Kimura, T., Varma, C. M., Subramanian, M. A., Cava, R. J., Ramirez, A. P.
The coupling between localized spins and phonons can lead to shifts in the dielectric constant of insulating materials at magnetic ordering transitions. Studies on isostructural SeCuO3...
Magneto-oscillations in Underdoped Cuprates (2008)
The conventional interpretation of the recent magneto-oscillation experiments in underdoped Cuprates, requires that there be a state of altered translational symmetry in the pseudogap state which is...
Long Wavelength Correlations and Transport in a Marginal Fermi Liquid (2008)
Marginal Fermi liquid was originally introduced as a phenomenological description of the cuprates in a part of the metallic doping range which appears to be governed by fluctuations due to a...
Gronsleth, M. S., Nilssen, T. B., Dahl, E. K., Stiansen, E. B., Varma, C. M., Sudbo, A.
We have performed large-scale Monte Carlo simulations on a two-dimensional generalized Ashkin-Teller model to calculate the thermodynamic properties in the critical region near its transitions. The...
Weak Ferromagnetism Accompanying Loop current order in Underdoped Cuprates (2008)
Aji, Vivek, Shekhter, Arkady, Varma, C. M.
We discuss the necessary symmetry conditions and the different ways in which they can be physically realized for the occurrence of ferromagnetism accompanying the loop current orbital magnetic order...
Shekhter, Arkady, Shu, Lei, Aji, Vivek, MacLaughlin, D. E., Varma, C. M.
We calculate the screening charge density distribution due to a point charge, such as that of a positive muon ($\mu^+$), placed between the planes of a highly anisotropic layered metal. In underdoped...
Josephson Effect for superconductors lacking time-reversal and inversion symmetries (2007)
Loridon, Brigette, Ng, Tai-Kai, Varma, C. M.
Physical Review Letters © copyright (2007) American Physical Society. The Journal's web site is located at http://prl.aps.org/
Universality of the single-particle spectra of cuprate superconductors (2007)
Zhu, Lijun, Aji, Vivek, Shekhter, Arkady, Varma, C. M.
All the available data for the dispersion and linewidth of the single-particle spectra above the superconducting gap and the pseudogap in metallic cuprates for any doping has universal features. The...
Theory of the Quantum Critical Fluctuations in Cuprates (2006)
The statistical mechanics of the time-reversal and inversion symmetry breaking order parameter, possibly observed in the pseudogap region of the phase diagram of the Cuprates, can be represented by...
The angle-resolved photoemission spectroscopy studies on cuprates in the pseudogap region reveal an extraordinary topological transition in which the ground state changes from one with a normal Fermi...
Coherence in the Two Kondo Impurity Problem (2006)
We show through a perturbative and an exact calculation using Wilson's renormalization methods that in the problem of two interacting Kondo impurities, on-site potential scattering generates a...
Josephson effect for superconductors lacking center of inversion (2006)
Leridon, Brigitte, Ng, Tai-Kai, Varma, C. M.
Due to the absence of a center of inversion in some superconducting compounds, a p-wave admixture to the dominant d-wave order parameter must exist. If time-reversal is also violated, an allowed...
Detecting Dichroism in Angle Resolved Photoemission (2006)
Recently, the time-reversal violation predicted for the pseudogap phase of the cuprates, which was observed by dichroism experiments using Angle-Resolved Photoemission has also been observed by...
Towards a complete theory of high T-c (2006)
Zaanen, J., Chakravarty, S., Senthil, T., Anderson, P., Lee, P., Schmalian, J., ...
Heavy-Fermions provide an extreme example of the utility of the idea of continuity and analyticity in physics. Their discovery and study in the past thirty years has added a fascinating chapter to...
A Theory of the Pseudogap State of the Cuprates (2005)
The phase diagram for a general model for Cuprates is derived in a mean-field approximation. A phase violating time-reversal without breaking translational symmetry is possible when both the ionic...
Helicity Order: Hidden Order Parameter in URu$_2$Si$_2$ (2005)
We propose that the "hidden order parameter" in URu$_2$Si$_2$ is a helicity order which must arise, if the Pomeranchuk criteria for the spin-antisymmetric Landau parameters with respect to the...
Deconstruction of the Kondo Effect near the AFM-Quantum Critical Point (2005)
Maebashi, H., Miyake, K., Varma, C. M.
The problem of a spin-1/2 magnetic impurity near an antiferromagnetic transition of the host lattice is solved. The problem is shown to transform to a multichannel problem. A variety of fixed points...
Developments in Correlated Fermions (2004)
This manuscript is based on the Summary and Overview talk given at the "The International Conference of Strongly Correlated Electronic Systems" (SCES '04), July 26-30, at Karlsruhe, Germany. After...
Some experimental signatures to look for time-reversal violating superconductors (2004)
We discuss some experimental signatures associated with the topological structures of unconventional superconductor order parameters of form dx2-y2+ix, where x = s, px±py, or dxy. Specifically, we...
Some Experimental Signatures to look for Time-reversal Violating superconductors (2004)
We discuss some experimental signatures associated with the topological structures of unconventional superconductor order parameters of form $d_{x^2-y^2}+ix$, where $x=s,p_x \pm p_y$, or $d_{xy}$....
Notes on RVB-Vanilla by Anderson et al (2003)
The claims made for the Resonating Valence Bond ideas for the cuprates in a recent paper by Anderson et al. on the basis of a variational calculation are discussed.
The cure to the $\ell=1$ Landau-Pomeranchuk (L-P) instabilities in translationally invariant fermions is shown to be a state with an anisotropic gap at the fermi-surface. For higher $\ell$ and for...
Angle Resolved Photemission Experiments to look for Time-reversal Violation in Cuprates (2003)
Campuzano, J. C., Kaminski, A., Varma, C. M.
The recent experiments reported by Borisenko et al. (cond-mat/0305179 v2), are examined in light of the conditions to be satisfied in the search for time-reversal violation by circularly polarized...
Kaminski, A., Rosenkranz, S., Fretwell, H. M., Campuzano, J. C., Li, Z. Z., Raffy, H., ...
In a recent comment [1], Armitage and Hu have suggested that our experiment observing dichroism in angle resolved photoemission (ARPES) [2] could not be conclusively interpreted as arising from time...
Lawes, G., Ramirez, A. P., Varma, C. M., Subramanian, M. A.
We report on the effects of spin fluctuations, magnetic ordering, and external magnetic field on the dielectric constant of the ferromagnet SeCuO3, and the antiferromagnet TeCuO3. A model based on...
Hall effect in the marginal Fermi liquid regime of high-Tc superconductors (2003)
The detailed derivation of a theory for transport in quasi-two-dimensional metals, with small-angle elastic scattering and angle-independent inelastic scattering is presented. The transport equation...
Electronic-vibrational coupling in single-molecule devices (2003)
Aji, Vivek, Moore, J. E., Varma, C. M.
Experiments studying vibrational effects on electronic transport through single molecules have observed several seemingly inconsistent behaviors, ranging from up to 30 harmonics of a vibrational...
Specific heat at the transition in a superconductor with fluctuating magnetic moments (2003)
Kos, Simon, Martin, Ivar, Varma, C. M.
In the heavy-fermion materials CeCoIn$_5$ and UBe$_{13}$, the superconducting order parameter is coupled to flucutating magnetization of the uncompensated part of the localized $f$-moments. We find...
Time-reversal and inversion breaking in the pseudogap region of the cuprate compounds have been proposed and detected by means of ARPES in the compound Bi-2212. Given the implication of the effect in...
A proposal to test the proposed time-reversal and inversion breaking phase in the Pseudogap region of the Cuprate compounds through the variation of Second-harmonic generation intensity with...
A proposal to determine the spectrum of pairing-glue in high-temperature superconductors (2002)
We propose a method for an analysis of the angle-resolved photoemission data in two-dimensional anisotropic superconductors which directly yields the spectral function of the bosons mediating Cooper...
Colossal Dielectric Constants in Braced Lattices with Defects (2002)
Ramirez, A. P., Lawes, G., Butko, V., Subramanian, M. A., Varma, C. M.
The dielectric constant of CaCu3Ti4O12 is measured with a different electrode geometry than previous measurements. Similar colossal values are obtained showing that they are "intrinsic" to the...
Spontaneous time reversal symmetry breaking in the pseudogap state of high-Tc superconductors (2002)
Kaminski, A., Rosenkranz, S., Fretwell, H. M., Campuzano, J. C., Li, Z., Raffy, H., ...
When matter undergoes a phase transition from one state to another, usually a change in symmetry is observed, as some of the symmetries exhibited are said to be spontaneously broken. The...
The equations in cond-mat/0011020 and Phys. Rev, Lett. 86, 4652 (2001) are valid but a numerical estimate in the paper is incorrect.
Detection and Implications of a Time-reversal breaking state in underdoped Cuprates (2002)
We present general symmetry considerations on how a Time-reversal breaking state may be detected by angle-resolved photoemission using circularly polarized photons as has been proposed earlier....
Higgs Boson in Superconductors (2001)
Superfluid helium, describable by a two-component order parameter, exhibits only the Bogolubov mode with energy $\to 0$ at long wavelengths, while a Lorentz-invariant theory with a two-component...
Singular Effects of Impurities near the Ferromagnetic Quantum-Critical Point (2001)
Maebashi, H., Miyake, K., Varma, C. M.
Systematic theoretical results for the effects of a dilute concentration of magnetic impurities on the thermodynamic and transport properties in the region around the quantum critical point of a...
Varma, C. M., Nussinov, Z., Van Saarloos, W.
An introductory survey of the theoretical ideas and calculations and the experimental results which depart from Landau Fermi-liquids is presented. Common themes and possible routes to the...
Ferroelectrics with Low-energy Electronic Excitations (2001)
We formulate a general theory of the dielectric response of a lattice with a structural transition and a polarization instability due to a soft-optic mode coupled to low energy electronic excitations...
Dynamics of some constrained lattices (2000)
We consider the dynamics of lattices which have constrained constitutive units flexible in only their mutual orientations. A continuum description is derived through which it is shown that the models...
We show that a scattering rate which varies with angle around the Fermi surface has the same effect as a periodic Lorentz force on magnetotransport coefficients. This effect, together with the...
Recent angular-resolved photoemission experiments on high-temperature superconductors are consistent with a phenomenological description of the normal state of these materials as Marginal Fermi...
Narimanov, E. E., Varma, C. M.
We develop a variational mean-field theory of the ferromagnetic transition in compounds like Lanthanum-Manganite within the framework of the Double-Exchange Model supplemented by modest disorder. We...
Proposal for an Experiment to Test a Theory of High Temperature Superconductors (1999)
A theory for the phenomena observed in Copper-Oxide based high temperature superconducting materials derives an elusive time-reversal and rotational symmetry breaking order parameter for the observed...
Magnetic Impurities in d-wave Superconductors (1999)
We solve the problem of a magnetic impurity in a $d_{x^2-y^2}$-wave superconductor by a variational method. A moment is found to exist in the superconducting state only if the Kondo-temperature in...
Pseudo-Gap Phase, the Quantum-Critical Point and superconductivity in Copper-Oxide Metals (1999)
A systematic solution of a general model for Copper-Oxides reveals a line of transitions $T = T_p (x)$ for $x$, the doping away from half-filling less than a critical value, to a phase with broken...
Heavy-Fermions in a Transition-Metal Compound: $LiV_2O_4$ (1999)
The recent discovery of heavy-Fermion properties in Lithium Vanadate and the enormous difference in its properties from the properties of Lithium Titanate as well as of the manganite compounds raise...
Polarizability and single particle spectra of two-dimensional s- and d-wave superconductors (1998)
We present analytic results for the polarizabilities, $\chi({\bf Q},\omega)$, in the charge, spin, and current channels for two-dimensional s- and d-wave superconductors for large momentum transfer....
Metal-Insulator Transition of Disordered Interacting Electrons (1998)
We calculate the corrections to the conductivity and compressibility of a disordered metal when the mean free path is smaller than the screening length. Such a condition is shown to be realized for...
Only Fermi-Liquids are Metals (1997)
Any singular deviation from Landau Fermi-liquid theory appears to lead, for arbitrarily small concentration of impurities coupling to a non-conserved quantity, to a vanishing density of states at the...
Tilting instability and other anomalies in the flux-lattice in some magnetic superconductors (1997)
The flux-line lattice in the compound $ErNi_2B_2C$, which has a tendency to ferromagnetic order in the a-b plane is studied with external magnetic field direction close to the c-axis. We show the...
Phonon Anomalies Induced by Superconductivity (1996)
We calculate the electronic polarizability in the superconducting state near extremum vectors ${\vec Q}_0$ of the Fermi surface. A pole appears in the polarizability at frequencies $\omega$ near the...
NMR in copper-Oxide Metals (1996)
The anomalous part of the NMR relaxation rate of coppernuclei in the normal state of copper-oxide metals is calculated using the orbital magnetic parts of the fluctuations derived in a recent theory...
Spontaneous vortex phase discovered? (1996)
It is argued that a spontaneous vortex phase may exist in the recently discovered compound $ErNi_2B_2C$ at temperature below 2.3K. The consequences of this proposal are discussed. In particular the...
Non Fermi-Liquid States and Pairing of a general Model of Copper-Oxide Metals (1996)
A model of copper-oxygen bonding and anti-bonding bands with the most general two-body interactions allowable by symmetry is considered. The model has a continuous transition as a function of...
Electronic and Magnetic States in the Giant Magneto-resistive Compounds (1996)
The paramagnetic insulator to ferromagnetic metal transition in Lanthanum manganites and the associated magnetoresistive phenomena is treated by considering the localization due to random hopping...
Anisotropy of the electron-phonon interaction in niobium. (1981)
Simons, A.L., Varma, C.M., Weber, W.
Physical Review B, 23(1981) S.2431-33
Phonon dispersion in transition metals. (1978)
Univ.Aarhus, Vortrag, Daenemark, 23.Juni 1978
Recent angular-resolved photoemission experiments on high-temperature superconductors are consistent with a phenomenological description of the normal state of these materials as marginal Fermi...
Recent angular-resolved photoemission experiments on high-temperature superconductors are consistent with a phenomenological description of the normal state of these materials as marginal Fermi...