Abstract

Low-dimensional spin systems are one of the actively studied subjects insolid state physics due to the possibility to observe numerous quantumphenomena and to interpret these phenomena within relatively simple models(e.g., Ising or Heisenberg models for different lattice types). Aninteresting phenomenon in spin physics is the formation of a spin liquid –a strongly correlated ground state lacking long-range magnetic order. Spinliquids originate from quantum fluctuations that are particularly strongin systems with reduced dimensionality and low spin value. Thefluctuations can be further enhanced by introducing magnetic frustrationwhich impedes long-range ordering of the system. This talk mainly focuseson frustrated two-dimensional square lattice systems.The spin-1/2 frustrated square lattice (FSL) is one of the simplest modelsgiving rise to a spin liquid ground state. In this model (also known asthe J1 − J2 model), magnetic moments on a square-lattice aresubjected to nearest-neighbor interaction J1 along the side of the squareand next-nearest-neighbor interaction J2 along the diagonal of the square.Extensive theoretical research on the FSL model has been done in the pastand a rich phase diagram has been proposed. Despite numerous theoreticalinvestigations, experimental realizations of the J1 − J2 modelcompounds are scarce. Recently we synthesized and investigated thephysical properties of two new compounds Pb2VO(PO4)2 and BaCdVO(PO4)2 viamagnetization, heat capacity, and nuclear magnetic resonance (NMR)measurements. These two compounds were found to be strongly frustrated J1− J2 square lattice compounds with ferromagnetic J1 andantiferromagnetic J2. Based on the frustration ratio J2/J1, BaCdVO(PO4)2(J2/J1 = 0.9) is placed more close to the quantum spin liquidregime of the phase diagram than the Pb2VO(PO4)2 (J2/J1 = 1.76).Both compounds undergo magnetic ordering at TN ≈ 1 K and 3.6 K,respectively, likely towards a columnar antiferromagnetic state. Using 31PNMR on a large single crystal we investigated the static and dynamicproperties of Pb2VO(PO4)2. From the NMR spectral measurements below TN, weobtained direct evidence for a columnar antiferromagnetic ground state.This ground state is consistent with the phase diagram, expected based onthe observed J2/J1 ratio.

Abstract

Besides supersymmetry, the other prime candidate of physics beyond the StandardModel (SM), crying out for verification at the CERN Large Hadron Collider (LHC), is extra-dimension. To hunt for effects of Kaluza–Klein (KK) excitations of known fermions and bosons is very much in the agenda of the LHC. These KK states arise when the SM particles access the extra space-like dimension(s). We consider here a 5-dimensional universal extra-dimension (UED) scenario. The Kaluza-Klein (KK) number is conserved at all tree level vertices. This entails the production of KK states in pairs and renders the lightest KK particle stable, which leaves the detector carrying away missing energy. The splitting between different KK flavors is controlled by the zero mode masses and the bulk- and brane-induced one-loop radiative corrections. We concentrate on the production of an n=1 KK electroweak gauge boson in association with an n=1 KK quark. This leads to a signal consisting of one jet, one or more leptons and missing pt. For definiteness we usually choose the inverseradius of compactification to be R1 = 500 GeV, which sets the scale of the lowest lying KK states. We show that with 10 fb1 integrated luminosity at the LHC with √s= 14 TeV this signal can be detected over the SM background by imposing appropriate kinematic cuts. We record some of the expectations for a possible intermediate LHC run at √s = 10 TeV and also exhibit the integrated luminosity required to obtain a 5 σ signal as a function of R1

Abstract

Cold atoms have emerged as a new and exciting platform to study thephysics of strongly interacting quantum many body systems relevant tocondensed matter physics. In this talk I will discuss how dynamics of coldatoms close to equilibrium can be used to reveal many body correlationsand detect novel phases in these systems. I will also discuss the dynamicsof these systems far from equilibrium, focusing on the relaxation of highenergy excitations in Fermionic systems.

Abstract

Modern magnetic devices (GMR read heads, magnetic sensors, hard disks andspintronics devices) relies on storing or manipulating magneticinformation in smaller length scales (nm’s) at faster time scales(nano-seconds to femto- seconds). It is very important to know themagnetic structure in order to understand the magnetic device. To advancenanoscience and nanotechnology, we have to be able to understand howmaterials behave at the nanoscale. Advancement of nano-science allows usto prepare structure in nanometer scale both by self-assembly and electronbeam lithography. X-ray magnetic characterization provide us informationon nanoscale with element specificity, chemical sensitivity, sensitivityto charge, orbital and spin ordering, high spatial resolution,polarization capability and faster time scales (dynamics using coherence,for coherent diffraction imaging and XPCS) and pump-probe techniques. Inthis talk I will present an overview of thin film magnetism and ultrafastmagnetic dynamics of magnetic multilayers exhibiting ordered stripes dueto perpendicular magnetic anisotropy (PMA). I will present a rather newand demanding technique to take image without a lens. One can see magneticstructure at the nanoscale level without using any lenses. One immediateapplication of this lens-less X-ray microscope is the development ofsmaller data storage devices for computers that can hold more memory.I will address the evolution of magnetic systems as a function of magnetic

Abstract