Structural disorder can lead to a localization of electron wave functions and metal-insulator transitions.

This gives rise to an enhancement of electron-electron interactions and to the appearance of local magnetic moments.

We investigate on heavily-doped semiconductors like crystalline P-doped Si (where disorder is introduced by the statistical distribution of P atoms) by measurements of the electrical resistance, Hall effect, specific heat, thermopower and magnetization at very low temperatures (down to 10 mK) in magnetic fields up to 9 T.

Individual P atoms can be identified by scanning tunneling microscopy and -spectroscopy.

The metal-insulator transition can be continuously tuned by application of uniaxial pressure to investigate the scaling of the electrical conductivity.

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In some rare-earth and actinide compounds, so called "heavy-fermion systems", the interaction between conduction electrons and 4f or 5f electrons gives rise to anomalous low-temperature properties. Many transition-metal compounds show strong electronic interactions as well.

Since these interactions strongly depend upon the interelectronic distance, different ground states (magnetic, non magnetic, or even superconducting) can occur as a function of external pressure or "chemical pressure", which is introduced by alloying with a third constituant of different atomic size.

Families of these alloys (e.g., CeCu₆, CeBiPt, MnSi) are investigated by measurements of the electrical resistivity, magnetization and specific heat, partly up to pressures of 20 kbar.

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Metallic layered systems, consisting of alternating superconducting and ferromagnetic layers are studied by measurements of the electronical resistance, the magnetic susceptibility and the magneto-optical Kerr effect to investigate the interplay between superconductivity and magnetism.

Thin metallic "bridges" (width down to 40 nm) between two metallic layers can be prepared by nanostructuring methods. At low temperatures, the electronical transport exhibits interference effects due to the coherence of the conduction-electron wave functions. Normal and superconducting bridges are investigated.

Contacts consisting of a few or only one atom can be prepared by breaking and reconnecting nanostructural bridges (width = 100 nm). The current through single atoms is investigated by means of the superconducting proximity effect.

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• Fermi-liquid instabilities at magnetic quantum phase transitions
  H. v. Löhneysen, A. Rosch, M. Vojta, P. Wölfle,
  Rev. Mod. Phys. 79 (2007) 1015

• Importance of in-plane anisotropy in the quasi-two-dimensional antiferromagnet BaNi₂V₂O₈,
  W. Knafo, C. Meingast, K. Grube, S. Drobnik, P. Popovich, P. Schweiss, P. Adelmann, Th. Wolf, H. v. Löhneysen,
  Phys. Rev. Lett. 99 (2007) 137206

• Magnetic fluctuations at a field-induced quantum phase transition
  O. Stockert, M. Enderle, H. v. Löhneysen,
  Phys. Rev. Lett. 99 (2007) 237203

• Partial order in the non-Fermi-liquid phase of MnSi
  C. Pfleiderer, D. Reznik, L. Pintschovius, H. v. Löhneysen, M. Garst, A. Rosch,
  Nature 427 (2004) 227-231

• Field-induced magnetic transition in heavy-fermion antiferromagnet Ce₇Ni₃
  K. Umeo, Y. Echizen, M. H. Jung, T. Takabatake, T. Sakakibara, T. Terashima, C. Terakura, C. Pfleiderer, M. Uhlarz, H. v.Löhneysen,
  Phys. Rev. B 67 (2003) 144408

• Magnetic phase diagram of CsCuCl₃ for in-plane magnetic fields up to 14 T
  R. Bügel, A. Faißt, H. v. Löhneysen, J. Wosnitza, U. Schotte,
  Phys. Rev. B 65 (2001) 052402

• Pressure versus magnetic field-tuning of a magnetic quantum phase transition
  H. v. Löhneysen, C. Pfleiderer, T. Pietrus, O. Stockert, B. Will,
  Phys. Rev. B 63 (2001) 134411

• Onset of antiferromagnetism in heavy-fermion metals
  A. Schröder, G. Aeppli, R. Coldea, M. Adams, O. Stockert, H. v. Löhneysen, E. Bucher, R. Ramazashvili, and P. Coleman,
  Nature 407 (2000) 351

• Phase transitions and non-Fermi-liquid behavior in UCu_5-xPd_x at low temperatures
  R. Vollmer, T. Pietrus, H. v. Löhneysen, R. Chau, M. B. Maple,
  Phys. Rev. B 61 (2000) 1218

• Fermi-liquid instability at magnetic-nonmagnetic quantum phase transitions
  H. v. Löhneysen,
  J. Magn. Magn. Mat. 200 532 (1999

Supraleitung

• Experimental verification of contact-size estimates in point-contact spectroscopy on superconductor / ferromagnet heterocontacts
  J. Gramich, P. Brenner, C. Sürgers, H. v. Löhneysen, G. Goll
  Phys. Rev. B 86 (2012) 155402

• Superconducting state of very thin Pd films deposited on a diluted insulating on Eu_xSr_1-xS ferromagnet
  A. Cosceev, C. Sürgers, H.-G. Boyen, P. Schweiss, H. v. Löhneysen
  Phys. Rev. B 83 (2011) 174516

• Spintronics in metallic superconductor/ferromagnet hybrid structures
  C. Sürgers, A. Singh, M. Stokmaier, G. Goll, F. Pérez-Willard, H. v. Löhneysen
  Feature Article, Int. J. Mat. Res. (formerly Z. Metallkd.) 101 (2010) 164

• Size dependence of current spin polarization through superconductor/ferromagnet nanocontacts
  M. Stokmaier, G. Goll, D. Weissenberger, C. Sürgers, H. v. Löhneysen,
  Phys. Rev. Lett. 101 (2008) 147005

• Spin-polarized current versus stray field in a perpendicularly magnetized superconducting spin switch
  A. Singh, C. Sürgers, R. Hoffmann, H. v. Löhneysen, T. V. Ashworth, N. Pilet, H. J. Hug,
  Appl. Phys. Lett. 91 (2007) 152504

• Competition between proximity-induced superconductivity and pair-breaking: Ag sandwiched between Nb an Fe
  H. Stalzer, A. Cosceev, C. Sürgers, H. v. Löhneysen,
  Phys. Rev. B 75 (2007) 224506

• Superconducting spin switch with perpendicular magnetic anisotropy
  A. Singh, C. Sürgers, H. v. Löhneysen,
  Phys. Rev. B 75 (2007) 024513

• Field-screening properties of proximity-coupled Nb/Ag double layers
  H. Stalzer, A. Cosceev, C. Sürgers, H. v. Löhneysen,
  Europhys. Lett. 76 (2006) 121

• Observation of interband pairing interaction in a two-band superconductor: MgB₂
  J. Geerk, R. Schneider, G. Linker, A. G. Zaitsev, R. Heid, K.-P. Bohnen, H. v. Löhneysen
  Phys. Rev. Lett. 94 (2005) 227005

• Evidence for crossed Andreev reflection in superconductor-ferromagnet hybrid structures
  D. Beckmann, H. B. Weber, H. v. Löhneysen,
  Phys. Rev. Lett. 93 (2004) 197003

• Inhomogeneous magnetization of a superconductiong film measured with a gradiometer
  H. Stalzer, A. Cosceev, C. Sürgers, H. v. Löhneysen,
  Appl. Phys. Lett. 84 (2004) 1522

• Low-temperature specific heat of the heavy-fermion superconductor PrOs₄Sb₁₂
  R. Vollmer A. Faißt, C. Pfleiderer, H. v. Löhneysen, E. D. Bauer, P.-C. Ho, V. Zapf, M. B. Maple,
  Phys. Rev. Lett. 90 (2003) 057001

• Superconducting energy gap distribution of MgB₂ investigated by point-contact spectroscopy
  F. Laube, G. Goll, J. Hagel, H. v. Löhneysen, D. Ernst, T. Wolf,
  Europhys. Lett. 56 (2002) 296

• Field-induced metal-insulator transition in a two-dimensional organic superconductor
  J. Wosnitza, S. Wanka, J. Hagel, H. v. Löhneysen, J. S. Qualls, J. S. Brooks, E. Balthes, J. A. Schlueter, U. Geiser, J. Mohtasham, R. W. Winter, G. L. Gard,
  Phys. Rev. Lett. 86 (2001) 508

• Spin-triplet superconductivity in Sr₂RuO₄ probed by Andreev reflection
  F. Laube, G. Goll, H. v. Löhneysen, M. Fogelström, F. Lichtenberg,
  Phys. Rev. Lett. 84 (2000) 1595

Eigenschaften von Legierungen seltener Erden

• Magnetic-field- and temperature-dependent Fermi surface of CeBiPt
  J. Wosnitza, G. Goll, A. D. Bianchi, B. Bergk, N. Kozlova, I. Opahle, S. Elgazzar, M. Richter, O. Stockert, H. v. Löhneysen, T. Yoshino, T. Takabatake,
  New J. Phys. 8 (2006) 174

• Low-temperature properties of YbAl₂
  T. Görlach, C. Pfleiderer, K. Grube, H. v. Löhneysen,
  Phys. Rev. B 71 (2005) 033101

• Magnetic-field-induced band-structure change in CeBiPt
  N. Kozlova, J. Hagel, M. Doerr, J. Wosnitza, D. Eckert, K.-H. Müller, L. Schultz, I. Opahle, S. Elgazzar, M. Richter, G. Goll, H. v. Löhneysen, G. Zwicknagl, T. Yoshino and T. Takabatake,
  Phys. Rev. Lett. 95 (2005) 086403

• Temperature-dependent Fermi surface in CeBiPt
  G. Goll, J. Hagel, H. v.Löhneysen, T. Pietrus, S. Wanka, J. Wosnitza, G. Zwicknagl, T. Yoshino, T. Takabatake,
  Europhys. Lett. 57 (2002) 233

• Pressure-induced residual resistivity anomaly in CeCu5Au
  H. Wilhelm, S. Raymond, D. Jaccard, O. Stockert, H. v. Löhneysen, A. Rosch,
  J. Phys.: Condens. Matter 13 (2001) L329 

Eigenschaften von metallischen Schichten, Schichtsystemen und Nanostrukturen

• Local strain-mapping on Ag(111) islands on Nb(110)
  T. Tomanic, C. Sürgers, R. Heid, M. Alcántara Ortigoza, K.-P. Bohnen, D. Stöffler, H. v. Löhneysen
  Appl. Phys. Lett. 101, 063111 (2012)

• Effect of cold working in a magnetic field on the shape of a ferromagnetic nanocontact
  M. Müller, R. Montbrun, C. Sürgers, H. v. Löhneysen
  Appl. Phys. Lett. 100, 202402 (2012)

• Formation of copper oxide surface structures via pulse injection of air onto Cu(111) surfaces
  C. Pérez León, Ch. Sürgers, H. v. Löhneysen
  Phys. Rev. B 85, 035434 (2012)

• Conductance tuning of Dy break-junctions by magnetostriction
  M. Müller, R. Montbrun, M. Marz, V. Fritsch, Ch. Sürgers, H. v. Löhneysen
  Nano Letters 11, 574-578 (2011)

• STM investigation of large p-conjugated oligomers and tetrahydrofuran codeposited on Cu(111) by pulse injection
  C. Pérez León, C. Sürgers, M. Mayor, M. Marz, R. Hoffmann, H. v. Löhneysen
  J. Phys. Chem. C 113 (2009) 14335

• Magnetic order by C-ion implantation into Mn5Si3 and Mn5Ge3 and its lateral modification
  C. Sürgers, N. Joshi, K. Potzger, T. Strache, W. Möller, G. Fischer, H. v. Löhneysen
  Appl. Phys. Lett. 93 (2008) 062503

• Electronic transport in magnetically ordered Mn₅Si₃C_x films
  B. Gopalakrishnan, C. Sürgers, A. Singh, R. Montbrun, M. Uhlarz, H. v. Löhneysen,
  Phys. Rev. B 77 (2008) 104414

• Identification of P dopants at non-equivalent lattice sites of the Si(111)-2x1 surface
  J. K. Garleff, M. Wenderoth, R.G. Ulbrich, C. Sürgers, H. v. Löhneysen. M. Rohlfing,
  Phys. Rev. B 76 (2007) 125322

• Correlations between one-dimensional structures at the Si(557):Au surface
  M. Sauter, R. Hoffmann, C. Sürgers, H. v. Löhneysen,
  Phys. Rev. B 75 (2007) 195436

• Correlation between transport properties and atomic configuration of atomic contacts of zinc by low-temperature measurements
  E. Scheer, P. Konrad, C. Bacca, A. Mayer-Gindner, H. v. Löhneysen, M. Häfner, J. C. Cuevas,
  Phys. Rev. B 74 (2006) 205430

• Atomically resolved tunneling spectroscopy on Si(557)-Au
  M. Schöck, C. Sürgers, H. v. Löhneysen,
  Europhys. Lett. 74 (2006) 473

• Evidence for one-dimensional electron propagation on Si(111)-(2x1) from Coulomb blockade
  J. K. Garleff, M. Wenderoth, R. G. Ulbrich, C. Sürgers, H. v. Löhneysen,
  Phys. Rev. B 72 (2005) 073406

• On the electron-phonon coupling of individual single-walled carbon nanotubes
  M. Oron-Carl, F. Hennrich, M. M. Kappes, H. v. Löhneysen, R. Krupke:
  Nano Letters 5 (2005) 1761

• Stable single-atom contacts of zinc whiskers
  P. Konrad, C. Bacca, E. Scheer, P. Brenner, A. Mayer-Gindner, H. v. Löhneysen,
  Appl. Phys. Lett. 86 (2005) 213115

• Determining the current polarization on Al/Co nanostructured point contacts
  F. Pérez-Willard, J. C. Cuevas, C. Sürgers, P. Pfundstein, J. Kopu, M. Eschrig, H. v. Löhneysen,
  Phys. Rev. B 69 (2004) 140502

• Mechanically controllable break-junctions for use as electrodes for molecular electronics
  T. Böhler, J. Grebing, A. Mayer-Gindner, H. v. Löhneysen and E. Scheer,
  Nanotechnology 15 (2004) S465

• Separation of metallic from semiconducting single-walled carbon nanotubes
  R. Krupke, F. Hennrich, H. v. Löhneysen, M. Kappes,
  Science 301 (2003) 344

• Low-temperature conductance measurements on single molecules
  J. Reichert, R. Ochs, H. B. Weber, M. Mayor, and H. v. Löhneysen,
  Appl. Phys. Lett. 82 (2003) 4137

• Driving current through single organic molecules
  J. Reichert, R. Ochs, D. Beckmann, H. B. Weber, M. Mayor, and H. v. Löhneysen,
  Phys. Rev. Lett. 88 (2002) 176804