Magnetotransport of Dirac Fermions on the surface of a topological insulator

We study the properties of Dirac fermions on the surface of a topological insulator in the presence of crossed electric and magnetic fields. We provide an exact solution to this problem and demonstrate that, in contrast to their counterparts in graphene, these Dirac fermions allow relative tuning of the orbital and Zeeman effects of an applied magnetic field by a crossed electric field along the surface. We also elaborate and extend our earlier results on normal metal-magnetic film-normal metal (NMN) and normal metal-barrier-magnetic film (NBM) junctions of topological insulators [Phys. Rev. Lett. {\bf 104}, 046403 (2010)]. For NMN junctions, we show that for Dirac fermions with Fermi velocity $v_F$, the transport can be controlled using the exchange field ${\mathcal J}$ of a ferromagnetic film over a region of width $d$. The conductance of such a junction changes from oscillatory to a monotonically decreasing function of $d$ beyond a critical ${\mathcal J}$ which leads to the possible realization of magnetic switches using these junctions. For NBM junctions with a potential barrier of width $d$ and potential $V_0$, we find that beyond a critical ${\mathcal J}$, the criteria of conductance maxima changes from $\chi= e V_0 d/\hbar v_F = n \pi$ to $\chi= (n+1/2)\pi$ for integer $n$. Finally, we compute the subgap tunneling conductance of a normal metal-magnetic film-superconductor (NMS) junctions on the surface of a topological insulator and show that the position of the peaks of the zero-bias tunneling conductance can be tuned using the magnetization of the ferromagnetic film. We point out that these phenomena have no analogs in either conventional two-dimensional materials or Dirac electrons in graphene and suggest experiments to test our theory.Comment: 11 pages, 12 figures; v

Tuning the conductance of Dirac fermions on the surface of a topological insulator

We study the transport properties of the Dirac fermions with Fermi velocity $v_F$ on the surface of a topological insulator across a ferromagnetic strip providing an exchange field ${\mathcal J}$ over a region of width $d$. We show that the conductance of such a junction changes from oscillatory to a monotonically decreasing function of $d$ beyond a critical ${\mathcal J}$. This leads to the possible realization of a magnetic switch using these junctions. We also study the conductance of these Dirac fermions across a potential barrier of width $d$ and potential $V_0$ in the presence of such a ferromagnetic strip and show that beyond a critical ${\mathcal J}$, the criteria of conductance maxima changes from $\chi= e V_0 d/\hbar v_F = n \pi$ to $\chi= (n+1/2)\pi$ for integer $n$. We point out that these novel phenomena have no analogs in graphene and suggest experiments which can probe them.Comment: v1 4 pages 5 fig

Emperipolesis in a Case of Adult T Cell Lymphoblastic Lymphoma (Mediastinal type)-Detected at FNAC and Imprint Cytology

Emperipolesis is a condition in which viable hematopoetic cells are seen intact in the cytoplasm of host cell without damage. This phenomenon is seen in many physiologic and pathologic conditions, its presence in Rosai Dorfman disease (RDD) is characteristic of the disease. However emperipolesis is an uncommon finding in malignant lymphoma both Hodgkins and non-Hodgkin’s lymphoma, wherein it has been described in bone marrow aspirate and tissue culture. In contrast there are only two case reports of emperipolesis phenomenon described in non-Hodgkin’s lymphoma in tissue sections. We report a case of an adult T cell lymphoblastic lymphoma (mediastinal type) with features of emperipolesis demonstrated at fine needle aspiration cytology (FNAC) and imprint cytology of cervical lymph nodes. To our knowledge, this is the first case report of emperipolesis in a case of adult T cell lymphoblastic lymphoma (mediastinal type)-detected at FNAC and imprint cytology

Magnetic phenomena at and near nu =1/2 and 1/4: theory, experiment and interpretation

I show that the hamiltonian theory of Composite Fermions (CF) is capable of yielding a unified description in fair agreement with recent experiments on polarization P and relaxation rate 1/T_1 in quantum Hall states at filling nu = p/(2ps+1), at and near nu = 1/2 and 1/4, at zero and nonzero temperatures. I show how rotational invariance and two dimensionality can make the underlying interacting theory behave like a free one in a limited context.Comment: Latex 4 pages, 2 figure

A stable Algebraic Spin Liquid in a Hubbard model

We show the existence of a stable Algebraic Spin Liquid (ASL) phase in a Hubbard model defined on a honeycomb lattice with spin-dependent hopping that breaks time-reversal symmetry. The effective spin model is the Kitaev model for large on-site repulsion. The gaplessness of the emergent Majorana fermions is protected by the time reversal (TR) invariance of this model. We prove that the effective spin model is TR invariant in the entire Mott phase thus ensuring the stability of the ASL. The model can be physically realized in cold atom systems and we propose experimental signals of the ASL.Comment: Published in PR

Herbal vs. Chemical Actives as Antidandruff Ingredients -Which Are More Effective in the Management of Dandruff?– An Overview

Dandruff, a clinical condition caused by Malassezia (Pityrosporum) species is of great cosmetic concern all over the world. Dandruff is known to be controlled by fungistatic ingredients in Anti-dandruff shampoos. A comparative study on the efficacy of chemical and herbal anti-dandruff ingredients on ‘as is’ basis and their performance in market shampoos was done in vitro against Pityrosporum ovale (MTCC 1374). Zinc pyrithione (ZnPTO), ketoconazole and other azole compounds recorded good anti-Pityrosporum activity among the chemical ingredients. Herbal ingredients like tea tree oil, rosemary oil, coleus oil, clove oil, pepper extract, neem extract, and basil extract also recorded anti-pityrosporum activity, but their MIC values are much higher than the synthetic ingredients. Shampoos containing ZnPTO and ketoconazole recorded higher in vitro activities than the shampoos containing herbal AD ingredients