jkfransson - Publications List

Ph.D. degree: (2002) physics; thesis | Non-orthogonality and Electron Correlations in Nanotransport. Spin- and Time-Dependent Currents; supervisor: Börje Johansson.

Docent: (2006) in Atomic, molecular, and condensed matter physics at Uppsala University.

Achievements: I have developed a diagrammatic Green function approach to treat nanoscale many-body systems under non-equilibrium conditions. Established a theory for asymmetries and negative differential conductance generated by strong electron correlations in nanoscale systems. Successfully provided a theoretical description and explanation for the so-called Pauli exclusion principle spin blockade in double quantum dot systems.

Future Position:
Senior Researcher funded by the Swedish Research Council (VR Rådsforskare) in Theory for Strongly Correlated Materials.
Physics Department, Uppsala University, Uppsala, Sweden
Begining in January 2008

Present position:
Patent Attorney Trainee, Awapatent AB, Stockholm.

Postdoc.:
2006 - 2007, (Mar. -06 - Jul. -07) Theoretical Division and Center for Nonlinear Studies (CNLS), Los Alamos National Laboratory (LANL), Los Alamos, USA. The position was sponsored by A. V. Balatsky (T-11, LANL) and A. M. N. Niklasson (T-1, LANL).

2006, (Jan. - Mar.) Physics Department, Uppsala University, Uppsala.

2005, Department of Materials Science and Engineering, KTH, Stockholm - Carl Trygger's Foundation.

2004, Department of Materials Science and Engineering, KTH, Stockholm.

2003, Physics Department, KTH, Stockholm.

2003 - 2005, Guest researcher at NORDITA, Copenhagen.

Abstract: We address Fano-like interference effects in scanning tunneling microscopy (STM) measurements of nanoscale systems, e.g. two-level systems. Common for these systems is that second order tunneling contributions give rise to interference effects that cause suppressed transmission through the system for certain energies. The suppressed transmission is measurable either in the differential conductance or in the bias voltage derivative thereof.

Abstract: We propose a mechanism to use scanning tunneling microscopy (STM) for direct measurements of the two-electron singlet-triplet exchange splitting $J$ in diatomic molecular systems, unsing the coupling between the molecule and the substrate electrons. The different pathways for electrons lead to interference effects and generate kinks in the differential conductance at the energies for the singlet and triplet states. These features are related to Fano resonance due to the branched electron wave functions. The ratio between the tunneling amplitudes through the two atoms can be modulated by spatial movements of the tip along the surface.

Abstract: Impurities that are present on the surface of a metal often have internal degrees of freedom. Inelastic scattering due to impurities can be revealed by observing local features seen in the tunneling current with scanning tunneling microscope (STM). We consider localized vibrational modes coupled to the electronic structure of a surface. We argue that vibrational modes of impurities produce Fermi momentum $k_F$ oscillations in second derivative of current with respect to voltage $\partial^2I(\bfr, V)/\partial V^2$. These oscillations are similar to the well known Friedel oscillations of screening charge on the surface. We propose to measure inelastic scattering generated by the presence of the vibrational modes with STM by imaging the $\partial^2I/\partial V^2$ oscillations on the metal surface.


Journal articles

2007	J Fransson (2007) Detection of exchange interaction in STM measurements through Fanolike interference effects Phys. Rev. B 76: 045416 July Abstract: We address Fano-like interference effects in scanning tunneling microscopy (STM) measurements of nanoscale systems, e.g. two-level systems. Common for these systems is that second order tunneling contributions give rise to interference effects that cause suppressed transmission through the system for certain energies. The suppressed transmission is measurable either in the differential conductance or in the bias voltage derivative thereof. Notes:
	M Pärnaste, M Marcellini, E Holmström, N Bock, J Fransson, O Eriksson, B Hjörvarsson (2007) Dimensionality crossover in the induced magnetization of Pd layers J. Phys.: Condens. Matter 19: 246243 May Abstract: Notes:
	J Fransson, A V Balatsky (2007) Exchange interaction and Fano resonances in diatomic molecular systems Phys. Rev. B 75: 153309 April Abstract: We propose a mechanism to use scanning tunneling microscopy (STM) for direct measurements of the two-electron singlet-triplet exchange splitting $J$ in diatomic molecular systems, unsing the coupling between the molecule and the substrate electrons. The different pathways for electrons lead to interference effects and generate kinks in the differential conductance at the energies for the singlet and triplet states. These features are related to Fano resonance due to the branched electron wave functions. The ratio between the tunneling amplitudes through the two atoms can be modulated by spatial movements of the tip along the surface. Notes:
	J Fransson, A V Balatsky (2007) Surface imaging of inelastic Friedell oscillations Phys. Rev. B 75: 195337 Abstract: Impurities that are present on the surface of a metal often have internal degrees of freedom. Inelastic scattering due to impurities can be revealed by observing local features seen in the tunneling current with scanning tunneling microscope (STM). We consider localized vibrational modes coupled to the electronic structure of a surface. We argue that vibrational modes of impurities produce Fermi momentum $k_F$ oscillations in second derivative of current with respect to voltage $\partial^2I(\bfr, V)/\partial V^2$. These oscillations are similar to the well known Friedel oscillations of screening charge on the surface. We propose to measure inelastic scattering generated by the presence of the vibrational modes with STM by imaging the $\partial^2I/\partial V^2$ oscillations on the metal surface. Notes:
2006	A V Balatsky, J Fransson, D Mozyrsky, Y Manassen (2006) STM NMR and nuclear spin noise Phys. Rev. B 73: 184429 May Abstract: We consider fluctuations of the electronic spin due to coupling to nuclear spin. Noise spectroscopy of an electronic spin can be revealed in the Scanning tunneling Microscope (STM). We argue that the noise spectroscopy of electronic spin can reveal the nuclear spin dynamics due to hyperfine coupling. tunneling current develops satellites of the main lines at Larmor frequency and at zero frequency due to hyperfine coupling. We also address the role of the rf field that is at or near the resonance with the nuclear hyperfine field. This approach is similar to Electron Nuclear Double Resonance (ENDOR), in that is allows one to detect nuclear spin dynamics indirectly through its effect on electronic spin. Notes:

	J Fransson, M Råsander (2006) Pauli spin blockade in weakly coupled double quantum dots Phys. Rev. B 73: 205333 May Abstract: In a two-level system, constituted by two serially coupled single level quantum dots, coupled to external leads we find that the current is suppressed in one direction of biasing caused by a fully occupied two-electron triplet state in the interacting region. The efficiency of the current suppression is governed by the ratio between the interdot tunnelling rate and the level off-set. In the opposite bias direction, the occupation of the two-electron triplet is lifted which allows a larger current to flow through the system, where the conductance is provided by transitions between one-electron states and two-electron singlet states. Is is also shown that a finite ferromagnetic interdot exchange interaction provides an extended range of the current suppression, while an anti-ferromagnetic exchange leads to a decreased range of the blockade regime. Notes:
	J Fransson (2006) Non-equilibrium triplet blockade in parallel coupled quantum dots New J. Physics 8: 114 July Abstract: It is theoretically demonstrated that parallel weakly tunnel coupled quantum dots exhibit non-equilibrium blockade regimes caused by a full occupation in the spin triplet state, in analogy to the Pauli spin blockade in serially weakly coupled quantum dots. Charge tends to accumulate in the two-electron triplet for bias voltages that support transitions between the singlet and three-electron states. Notes:
	J -X Zhu, J Fransson (2006) Electric field control of spin dynamics in a magnetically active tunnel junction J. Phys.: Condens. Matter 18: 9929 Oct Abstract: The dynamics of a single spin embedded in a tunneling junction is studied. Within a nonequilibrium Keldysh Green's function technique, we derive a quantum Langevin equation describing the spin dynamics. At high temperature limit, it reduces to a Bloch equation, for which the spin relaxation rate as determined by the temporal fluctuation is linearly proportional to the temperature. In the opposite limit, the relaxation rate depends on the applied voltage, in contrast to the case of a spin in an equilibrium environment. We also show that spin-flip transition processes during the electron tunneling converts the applied electric field (i.e., voltage bias) into an effective magnetic field. Consequently, the dynamics of the spin, otherwise precessing along the static magnetic field, will have either a frequency shift proportional to the dc bias or a magnetic resonance driven indirectly by an ac electric field at the Larmor frequency $\omega_{L}$. An experiment to measure this effect is also proposed. Notes:
	J Fransson (2006) Formation of pure two-electron triplet states in weakly coupled quantum dots attached to ferromagnetic leads Nanotechnology 17: 5344 Oct Abstract: Weakly coupled quantum dots in the Pauli spin blockade regime are considered with respect to spin-dependent transport. By attaching one half-metallic and one non-magnetic lead, the Pauli spin blockade if formed by a pure triplet state with spin moment $S=1$ or $S=-1$. Furthermore, additional spin blockade regimes emerge because of full occupation in states with opposite spin to that of the half-metallic lead. Notes:
	J Fransson, O Bengone, J A Larsson, J C Greer (2006) Combining Mesoscopic Models of Transport and First Principle Calculations for Molecular Electronic Transport IEEE Transactions on Nanotechnology 5: 745 Nov Abstract: Notes:
2005	J Fransson (2005) Angular conductance resonances of quantum dots strongly coupled to noncollinearly oriented ferromagnetic leads Phys. Rev. B 72: 045415 July Abstract: Notes:
	J Fransson (2005) Angular conductance resonances of quantum dots non-collinearly coupled to ferromagnetic leads Europhys. Lett. 70: 796 May Abstract: Notes:
	J Fransson (2005) Non-equilibrium theory for quantum dot with arbitrary on-site correlation strength coupled to leads Phys. Rev. B 72: 075314 Aug Abstract: Notes:
	J Fransson, J -F Lin, L Rotkina, J P Bird, P A Bennett (2005) Signatures of Band-Like Tunnelling in Granular Nanowires Phys. Rev. B 72: 113411 Sept Abstract: Notes:
2004	J Fransson, O Eriksson (2004) Asymmetric negative differential conductance in double quantum dots J. Phys.: Condens. Matter 16: L85 Feb Abstract: Notes:

	J Fransson (2004) Theory of current-voltage asymmetries in double quantum dots Phys. Rev. B 69: 201304(R) May Abstract: Notes:
	J Fransson, I Sandalov, O Eriksson (2004) A perfect spin-filter quantum dot system J. Phys.: Condens. Matter 16: L249 April Abstract: Notes:
	O Bengone, O Eriksson, J Fransson, I Turek, J Kudronovsky, V Drachl (2004) Electronic structure and transport properties and CrAs/GaAs/CrAs multilayers from first principles theory Phys. Rev. B 70: 035302 July Abstract: Notes:
	J Fransson, O Eriksson (2004) Current-voltage asymmetries and negative differential conductance due to strong electron correlations in double quantum dots Phys. Rev. B 70: 085301 Aug Abstract: Notes:
2003	J Fransson, E Holmström, O Eriksson, I Sandalov (2003) Theory of spin-filtering through quantum dots Phys. Rev. B 67: 205310 May Abstract: Notes:
2002	J Fransson, O Eriksson, I Sandalov (2002) Many-Body Approach to Spin-Dependent Transport in Quantum Dot Systems Phys. Rev. Lett. 88: 226601 May Abstract: Notes:
	J Fransson, O Eriksson, I Sandalov (2002) Effects of non-orthogonality and electron correlations on the time-dependent current through quantum dots Phys. Rev. B 66: 195319 Nov Abstract: Notes:
2001	J Fransson, O Eriksson, I Sandalov (2001) Effects of nonorthogonality in the time-dependent current through tunnel junctions Phys. Rev. B 64: 153403 Sept Abstract: Notes:
1999	J Fransson, O Eriksson, B Johansson, I Sandalov (1999) On the non-orthogonality problem in the description of quantum devices Physica B 272: 28 Dec Abstract: Notes:

Journal articles