27 research outputs found
Global superfluid phase diagram of a three component fermions with magnetic ordering
We investigate a three-component fermion mixture in the presence of weak attractive interactions. We use a combination of the equation of motion and the Gaussian variational mean-field approaches, which both allow for simultaneous superfluid and magnetic ordering in an unbiased way, and capture the interplay between the two order parameters. This interplay significantly modifies the phase diagram, especially the superfluid-normal phase boundaries. In the close vicinity of the critical temperature and for small chemical potential imbalances, strong particle-hole symmetry breaking leads to a phase diagram similar to the one predicted by Cherng, however, the overall phase diagram is markedly different: additional chemical potential-driven first- and second-order transitions and triple points emerge as well as more exotic second-order multicritical points, and bicritical lines with O(2,2) symmetry. We identify the terms which are necessary to capture this complex phase diagram in a Ginzburg-Landau approach, and determine the corresponding coefficients. © 2012 American Physical Society
Generalized Gibbs ensemble and work statistics of a quenched Luttinger liquid
We analyze the probability distribution function (PDF) of work done on a Luttinger liquid for an arbitrary finite duration interaction quench and show that it can be described in terms of a generalized Gibbs ensemble. We construct the corresponding density matrix with explicit intermode correlations, and determine the duration and interaction dependence of the probability of an adiabatic transition and the PDF of nonadiabatic processes. In the thermodynamic limit, the PDF of work exhibits a non-Gaussian maximum around the excess heat, carrying almost all the spectral weight. In contrast, in the small system limit most spectral weight is carried by a delta peak at the energy of the adiabatic process, and an oscillating PDF with dips at energies commensurate to the quench duration and with an exponential envelope develops. Relevance to cold atom experiments is also discussed
Hibrid mágneses szerkezetek = Hybrid magnetic structures
Hibrid mágneses szerkezetek' c. pályázatunkban kĂ©t tĂ©makörben: (i) a mágneses nanostruktĂşrák ab initio szintű vizsgálatában Ă©s (ii) a mágneses fĂ©lvezetĹ‘k valamint a kvantumszennyezĹ‘k tanulmányozásában vĂ©geztĂĽnk intenzĂv elmĂ©leti kutatásokat: (i) Atomcsoportok Ă©s ultravĂ©kony filmek mágneses szerkezetĂ©t határoztuk meg, rávilágĂtva a Dzyaloshinskii-Moriya kölcsönhatás jelentĹ‘sĂ©gĂ©re. A nagysűrűsĂ©gű mágneses adattárolás szempontjábĂłl meghatározĂł mágneses anizotrĂłpia kontroll-mechanizmusait vizsgáltuk vĂ©konyrĂ©tegekben. Kidolgoztuk a mágneses anizotrĂłpia energia hĹ‘mĂ©rsĂ©kletfĂĽggĂ©sĂ©nek ab initio elmĂ©letĂ©t. RĂ©szletesen tanulmányoztuk az áram által hajtott spinátfordulás jelensĂ©gĂ©t Ă©s a magneto-optikai Kerr effektust; (ii) Rámutattunk a nem-kollineáris állapotok kialakulására GaMnAs hĂg mágneses fĂ©lvezetĹ‘ben Ă©s skálaelmĂ©letet dolgoztunk ki a magnetotranszport leĂrására. Ăšj mechanizmust javasoltunk egy Kondo szennyezĹ‘ felĂĽleti mágneses anizotrĂłpiájára. RĂ©szletesen vizsgáltuk a spin szennyezĂ©sek elektron koherenciára gyakorolt hatását, a spinek relaxáciĂłját Ă©s a kvantum dot rendszerek dinamikáját. Pályázatunk elsĹ‘sorban az alapkutatásba sorolhatĂł, bár a nanomágnessĂ©g Ă©s spintronika terĂĽletĂ©n több alkalmazás orientált eredmĂ©nyĂĽnk szĂĽletett (pl. komplex vĂ©konyrĂ©tegek mágneses anizotrĂłpiája, áram által hajtott spinátfordulás, magnetotranszport mágneses fĂ©lvezetĹ‘kben). | In our research project entitled 'Hybrid magnetic structures' we performed intensive theoretical research on (i) magnetic nanostructures and (ii) on magnetic semiconductors and quantum impurities: (i) By highlighting the role of the Dzyaloshinskii-Moriya interactions, we determined the magnetic structure of small atomic clusters and ultrathin films. We carefully investigated the control of magnetic anisotropy that is of primary importance for high-density magnetic recording. We developed a first principles theory for the temperature dependence of the magnetic anisotropy energy. We also studied the phenomena of current driven magnetization switching and magneto-optical Kerr effect; (ii) We pointed out the formation of non-collinear states in GaMnAs magnetic semiconductor and developed a scaling theory for the description of magnetotransport. We proposed a novel mechanism for the surface magnetic anisotropy of Kondo impurities. We performed detailed studies on the effect of spin-impurities to electron coherence, on the relaxation spins and the dynamics of quantum dot systems. Although the results of our project mainly concern fundamental research, some of them, such as the magnetic anisotropy of ultrathin films, current induced spin-switching, magnetotransport in magnetic semiconductors, might be useful for applications in nanomagnetism and spintronics
Korrelációk és rendezetlenség mezoszkópikus és erősen korrelált rendszerekben = Correlation effects and disorder in mesoscopic and strongly correlated systems
Kutatásaink egy rĂ©szĂ©ben mezoszkĂłpikus rendszerek viselkedĂ©sĂ©t tanulmányoztunk, ahol mind az elektron-elektron kölcsönhatás, mind pedig a rendezetlensĂ©g ill. a rendszerspecifikus aprĂł rĂ©szletek fontos szerepet játszanak esetĂĽkben. A kutatás cĂ©lja ezeknek a tulajdonságoknak egyĂĽttes tanulmányozása volt. Egyik fĹ‘ cĂ©lunk a szennyezĂ©sek ill. a koherenciát erĹ‘sen befolyásolĂł inelasztikus folyamatok megĂ©rtĂ©se volt. MásfelĹ‘l kvantum pöttyökben fellĂ©pĹ‘ egzotikus korrelált állapotokat vizsgáltunk kutatásaink során. A projekt másik fĹ‘ cĂ©lkitűzĂ©sekĂ©nt rendezetlen rendszerekbeli korreláciĂłs effektusokat, a fĂ©m-szigetelĹ‘ fázisátalakulás számos vonását, Ă©s korreláciĂł-indukálta kvantum fázisátalakulásokat tanulmányoztunk numerikus Ă©s analĂtikus mĂłdszerekkel. Itt kutatásaink elsĹ‘sorban a fĂ©lvezetĹ‘ rendszerekbeli Mott-Anderson átalakulásra ill. a mágnessĂ©g Ă©s a rendezetlensĂ©g mágneses fĂ©lvezetĹ‘kbeli összefĂĽggĂ©sĂ©nek tanulmányozására irányultak. Az OTKA projekthez kapcsolĂłdĂłan mintegy 44 publikáciĂłnk jelent meg, közĂĽlĂĽk 12 a Physical Review Letters hasábjain 20 pedig a Physical Review B-ben. Ezekre a közlemĂ©nyekre már eddig is több mint 200 fĂĽggetlen hivatkozás Ă©rkezett. A rĂ©sztvevĹ‘ kutatĂłk mintegy fĂ©lszáz meghĂvott elĹ‘adást tartottak nemzetközi konferenciákon ill. kĂĽlföldi kutatási intĂ©zmĂ©nyekben. A kutatáshoz kapcsolĂłdĂłan öt diplomamunka, egy Ph.D. Ă©rtekezĂ©s, Ă©s egy akadĂ©miai doktori disszertáciĂł szĂĽletett. | Part of our research focused on the study of mesoscopic systems. In these small structures the electron-electron interaction as well as disorder and sample-specific details play an essential role. Our main goal was to study these effects and their interplay. One of our main goals was to understand how impurities affect inelastic processes and lead to the destruction of coherence. On the other hand, we studied exotic correlated states which form in mesoscopic quantum dot structures. The other main objective of this research project was to study disordered systems, several aspects of the metal-insulator transition, and correlation-induced quantum phase transitions using a variety of analytical and numerical methods. This part of the project focused mostly on the Mott-Anderson transition in semiconductor systems and the interplay of magnetism and localization effects in ferromagnetic semiconductors. Related to the project, a total of 44 publications appeared, 12 of them in the Physical Review Letters, and another 20 in the Physical Review B. So far we received over 200 independent citations for these publications. The participants of the project gave over 50 invited talks on international conferences and schools, and in international research institutions. Five diploma thesis, a Ph.D. thesis and a (D.Sc., i.e. Doctor of the Academy of Sciences) dissertation have been written and defended as part of this research project
Fermi liquid theory of resonant spin pumping
We study resonant all-electric adiabatic spin pumping through a quantum dot with two nearby levels by using a Fermi liquid approach in the strongly interacting regime, combined with a projective numerical renormalization group (NRG) theory. Due to spin-orbit coupling, a strong spin pumping resonance emerges at every charging transition, which allows for the transfer of a spin similar to h/2 through the device in a single pumping cycle. Depending on the precise geometry of the device, controlled pure spin pumping is also possible
Konzorcium, fő p.: Kvantum fázisok és fázisátalakulások hangolható korrelált rendszerekben = Consortional main: Quantum phases and phase transitions in tunable correlated systems
A pályázat cĂ©lja egyfelĹ‘l mezoszkĂłpikus áramkörökbeli korrelált állapotok tanulmányozása volt nem egyensĂşlyi körĂĽlmĂ©nyek között, másfelĹ‘l pedig ultrahideg atomi rendszerek illetve korrelált modellek egzotikus állapotainak feltĂ©rkĂ©pezĂ©sĂ©t tűztĂĽk ki cĂ©lul. KiemelkedĹ‘ek a rendezetlen kvantum rendszerek lokalizált illetve ĂĽveg állapotainak leĂrására vonatkozĂł eredmĂ©nyek, az SU(N) Mott szigetelĹ‘k kvantum fázisaira vontakozĂł eredmĂ©nyeink, a kölcsönhatĂł rendszerekbeli kvantum kvencs számĂtások eredmĂ©nyei, az U(1) spin folyadĂ©kokra vonatkozĂł eredmĂ©nyeink, valamint a nem egyensĂşlyi rendszerek zaj spektrumára vonatkozĂł - kĂsĂ©rletileg is igazolt eredmĂ©nyek. A kutatás eredmĂ©nyekĂ©pp többek között 11 Physical Review Letters közlemĂ©ny, 1 Physical Review X, 1 Nanoscale publikáciĂł Ă©s 39 Physical Review cikk szĂĽletett. A kutatĂłmunkába 11 diák kapcsolĂłdott be, munkájuk nyomán 7 dĂjazott TDK dolgozat, 4 BSc diplomamunka, 4 MSc diplomamunka Ă©s 3 doktori disszertáciĂł szĂĽletett. | The goal of this proposal was to study correlated states of mesoscopic circuits under non-equilibrium conditions, on the one hand, and to search for novel exotic quantum states of tunable cold atomic systems and other correlated systems, and to characterize these states, on the other hand. Of special importance are our results regarding the various quantum phases of SU(N) Mott insulators, the results concerning the description of localized and glassy states of disordered quantum systems, the characterization of U(1) spin liquid states, our studies of quantum quench in interacting many-body systems, and finally, the theoretical results regarding the non-equilibrium noise spectrum in correlated mesoscopic circuits - also confirmed experimentally. Among others, the research project resulted in 11 Physical Review Letters, one Physical Review X, one Nanoscale, and 39 Physical Review publications. Eleven students were integrated into this project, and their devoted research resulted so far in 7 (awarded) student's research project (TDK), 4 BSc theses, 4 MSc theses, and 3 PhD dissertations
Nem egyensúlyi spin transzport és korrelációk nanostruktúrákban = Out-of-equilibrium spin transport and correlations in nanoscale structures
A projekt atomi Ă©s mestersĂ©ges atomi struktĂşrák illetve felĂĽletek, vĂ©kony rĂ©tegek vizsgálatát cĂ©lozta ab initio illetve tĂ©relmĂ©leti mĂłdszerek egyĂĽttes használatával, kĂĽlönös tekintettel a mágneses tulajdonságokra illetve az idĹ‘ Ă©s spinfĂĽggĹ‘ nem egyensĂşlyi transzporttulajdonságokra. CĂ©ljaink között szerepelt egyfelĹ‘l olyan nem egyensĂşlyi mĂłdszerek alkalmazása/fejlesztĂ©se Ă©s egyszerű rendszerekbeli tesztelĂ©se, mely lehetĹ‘vĂ© teszi korrelált rendszerekben az egyensĂşlyi Ă©s nem egyensĂşlyi transzport leĂrását. Kiemelt szerepet kapott egy felxibilis numerikus renormálási csoport kĂłd kifejlesztĂ©se, publikálása Ă©s alkalmazása, illetve nem egyensĂşlyi közelĂtĂ©sek kidolgozása. Kutatásunk további fontos komponense volt a kvantum dot rendszerek, atom-klaszterek, nanoszemcsĂ©k, mágneses szennyezĹ‘k, dinamikai tulajdonságainak (ac vezetĹ‘kĂ©pessĂ©g, zaj spektrum) vizsgálata, illetve vĂ©kony rĂ©tegek Ă©s felĂĽletek transzport Ă©s mágneses tulajdonságainak elmĂ©leti vizsgálata. KĂĽlönös figyelmet szenteltĂĽnk a spin-pálya kölcsönhatás indukálta effektusok, Ăgy a felĂĽleti mágneses anizotrĂłpia, a spin-pálya kölcsönhatás indukálta spin relaxáciĂł, az anomális Hall effektus Ă©s a spin Hall effektus tanulmányozásának. A projekthez kapcsolĂłdĂłan majd 50 publikáciĂł szĂĽletett, közöttĂĽk 9 megjelent Physical Review Letters, Ă©s 23 Physical Review B publikáciĂł, kĂ©t 2 PhD disszertáciĂł, valamint egy nyilvános flexibilis NRG programcsomag a hozzá tartozĂł dokumentáciĂłval [http://www.phy.bme.hu/~dmnrg/]. | The main goal of this project was to combine ab initio and field theoretical methods to study and understand the properties of atomic clusters, artificial atomic structures and surfaces, with special emphasis on spin- and time-dependent and non-equilibrium transport properties. Among others, we developed theoretical tools which we tested on simple systems, and used to study dynamical and non-equilibrium transport properties of correlated systems. Some of the main technical achievements of this project were the development and application of a flexible open-access numerical renormalization group code, and the elaboration of approximate non-equilibrium methods. Besides the methodological development, our research mainly focused on ac transport properties and noise spectra of quantum dot systems and of clusters of magnetic atoms, and aimed at the characterization of the properties of magnetic impurities and clusters in the vicinity of a surface and in nano-grains. We also studied a wide range of spin-orbit coupling-induced phenomena in systems of reduced dimension such as surface anisotropy, spin-orbit interaction induced spin relaxation, anomalous and spin Hall effects, and magnetic states. Close to 50 publications emerged as a result of this project, including 2 PhD dissertations, 9 Physical Review Letters, and 23 Physical Review B papers, an open access computer package with complete documentation [http://www.phy.bme.hu/~dmnrg/]
Superdiffusive quantum work and adiabatic quantum evolution in finite temperature chaotic Fermi systems
We study the full distribution of quantum work in generic, noninteracting, disordered fermionic nanosystems at finite temperature. We derive an analytical determinant formula for the characteristic function of work statistics for quantum quenches starting from a thermal initial state. For work small compared to the thermal energy of the Fermi gas, work distribution is Gaussian, and the variance of work is proportional to the average work, while in the low-temperature or large-work limit, a non-Gaussian distribution with superdiffusive work fluctuations is observed. Similarly, the time dependence of the probability of adiabaticity crosses over from an exponential to a stretched exponential behavior. For large enough average work, the work distribution becomes universal, and depends only on the temperature and the mean work. Apart from initial low-temperature transients, work statistics are well captured by a Markovian energy-space diffusion process of hardcore particles, starting from a thermal initial state. Our findings can be verified by measurements on nanoscale circuits or via single qubit interferometry