Publications

Can mesoscopic shot noise experiments show the doubling of the charge carriers in a superconductor? Turns out, it’s complicated. We investigated this in several different samples, and made predictions as to what is necessary to make this work.

Jiasen Niu, Koen M. Bastiaans, Jianfeng Ge, Ruchi Tomar, John Jesudasan, Pratap Raychaudhuri, Max Karrer, Reinhold Kleiner, Dieter Koelle, Arnaud Barbier, Eduard F.C. Driessen, Yaroslav M. Blanter, Milan P. Allan

Phys. Rev. Lett. 132, 076001 (Editors’ Suggestion)

Shot noise has been suggested for a long time as a tell-tale probe for Majorana bound states. We are the first to carry out local tunneling shot noise measurements on the putative vortex Majorana states.

J-F Ge, KM Bastiaans, D Chatzopoulos, D Cho, WO Tromp, T Benschop, J Niu, G Gu, MP Allan

Nature Communications 4, 3341 (2023)

See news item by Michelle Willebrands

Why does cuprate superconductivity break down at a certain doping level? Using scanning tunneling spectroscopy we find that an emerging metallic matrix inside the superconducting state is responsible for the overall reduction of Tc and the superfluid density, while leaving the gapsize unchanged. The formation of the matrix is tied to a pair breaking process violating a core principle of mean-field theories.

WO Tromp, T Benschop, J-F Ge, I Battisti, KM Bastiaans, D Chatzopoulos, A Vervloet, S Smit, E van Heumen, MS Golden, Y Huang, T Kondo, Y Yin, JE Hoffman, MA Sulangi, J Zaanen, MP Allan

Nature Materials 22, 703 (2023)

See News and Views by Yu He.

We use our atomic-scale scanning tunneling noise setup on a disordered superconductor, and discover a state above TC that, much like an ordinary metal, has no (pseudo)gap, but carries charge via paired electrons.

KM Bastiaans, D Chatzopoulos, J-F Ge, D Cho, WO Tromp, JM van Ruitenbeek, MH Fischer, PJ de Visser, DJ Thoen, EFC Driessen, TM Klapwijk, MP Allan

Science 374, 608 (2021)

Featured as ‘Research Highlight’ in Nature Physics by David Abergel

See Physics World, SRON news, TU Delft news, Leiden news.

Why is there so much variation in TBG devices? And are open devices more disordered than encapsulated ones? We introduce a new method to continuously map inhomogeneities of a moiré lattice and apply it to open-device TBG to show that twist angle variation is small over areas of hundreds of nm.

T Benschop , TA de Jong, P Stepanov*, Xiaobo Lu, V Stalman, SJ van der Molen, DK Efetov, MP Allan

Phys. Rev. Research 3, 013153 (2021)

See also Nat Comm with the group of van der Molen

We report on a peculiar, spatially dispersing YSR state in Fe(Se,Te) that can be tuned by the tip.

D Chatzopoulos, Doohee Cho, KM Bastiaans, GO Steffensen, D Bouwmeester, A Akbari, Genda Gu, J Paaske, BM Andersen, MP Allan

Nature Communications 12, 298 (2021)

A first paper from the TBG collaboration is online, with beautiful data from the Baumberger group in Geneva, and great devices from the Efetov group at ICFO. We measured STM on the device.

S Lisi, X Lu, T Benschop, TA de Jong, Petr S, JR Duran, F Margot, I Cucchi, E Cappelli, A Hunter, A Tamai, V Kandyba, A Giampietri, A Barinov, J Jobst, V Stalman, M Leeuwenhoek, K Watanabe, T Taniguchi, L Rademaker, SJ van der Molen, MP Allan, DK Efetov, F Baumberger

Nature Physics 17, 198 (2020)

News coverage by NRC

We directly test the consistency of results from these three techniques by comparing data from the correlated metal Sr2RhO4. Using ARPES, STM, and quantum oscillations, we find good agreement for the Fermi surface topography and carrier effective masses. Hence, the apparent absence of such an agreement in other quantum materials, including the cuprates, suggests that the electronic states in these materials are of different, non-Fermi liquid-like nature. Collaboration with the groups of Baumberger, Perry, and Mackenzie.

I Battisti, WO Tromp, S Riccò, RS Perry, AP Mackenzie, A Tamai, F Baumberger, MP Allan

npj Quantum Materials 5, 91 (2020)

We succeeded in measuring the superfluid density with atomic resolution on an unconventional superconductor! In contrast to expectations for conventional superconductors, we find that the superfluid densisty is strongly inhomogeneous in FeTe0.55Se0.45.

D Cho* & KM Bastiaans* & D Chatzopoulos*, GD Gu, MP Allan

Nature 571, 541 (2019)

We introduce a platform for bringing new, device-based functionality to STM, with the goal of utilizing decades of progress in device engineering for the field of scanning probe.

M Leeuwenhoek, RA Norte, KM Bastiaans, Doohee Cho, I Battisti, YaM Blanter, S Gröblacher, MP Allan

Nanotechnology 30, 335702 (2019)

See also our papers on the theoretical modeling of such measurements, and the paper about fabrication.

We have imaged the doubling of the current noise due to Andreev reflections in a Josephson scanning tunneling microscope.

KM Bastiaans, D Cho, D Chatzopoulos, M Leeuwenhoek, C Koks, MP Allan

Phys. Rev. B 100, 104506 (2019)

Our first completely home-built STM is alive! And it has the world’s highest resonance frequency.

I Battisti, G Verdoes, K van Oosten, KM Bastiaans, and MP Allan

Rev. Sci. Instrum. 89, 123705 (2018)

Using our newly developed noise-spectroscopy technique we discover charge trapping in a cuprate high-temperature superconductor.

KM Bastiaans* & D Cho*, T Benschop, I Battisti, Y Huang, MS Golden, Q Dong, Y Jin, J Zaanen, MP Allan

Nature Physics 14, 1183 (2018)

Instrument details in Rev. Sci. Instrum. 89, 093709 (2018)

See also quantum universe (in dutch), Phys.org , Leiden University news, UvA news.

We propose an approach to transform a ‘pristine’ material into a better (meta-) superconductor by making use of modern fabrication techniques – designing and engineering the electronic properties of thin films via periodic patterning on the nanoscale.

MP Allan, MH Fischer, O Ostojic, A Andringa

SciPost Phys. 3, 010 (2017)

We discover of electronic order, pseudo gap phase separation and an impurity-band Mott transition in an iridate compound, cuprate-style. Along the way, we gained unique knowledge on how a Mott state collapses.

I. Battisti* & K.M. Bastiaans*, V. Fedoseev, A. de la Torre, N. Iliopoulos, A. Tamai, E.C. Hunter, R.S. Perry, J. Zaanen, F. Baumberger, M.P. Allan

Nature Physics 13, 21 (2017)

See also Leiden University news by Erik Arends, Phys.org

Both the density of states and the QPI dispersion of LiFeAs shows signatures of electron-boson coupling. Comparing these with fingerprints of different boson couplings to conclude that these signatures stem from AF spin fluctuations.

MP Allan* & Kyungmin Lee* & AW Rost*, MH Fischer, F Massee, K Kihou, C-H Lee, A Iyo, H Eisaki, T-M Chuang, AP Mackenzie, JC Davis, DJ Scalapino, E-A Kim

Nature Physics 11, 177 (2015)

See also Cornell Chronicle by Anne Ju, Phys.org

The heavy Fermion superconductor CeCoIn5 has a d-wave gap with nodes along the (1,1) direction, as we find using QPI.

MP Allan* & F Massee*, DK Morr, J van Dyke, AW Rost, AP Mackenzie, C Petrovic, JC Davis

Nature Physics 9, 468 (2013)

Featured in ‘News and Views’ by L Taillefer

See also Phys.org, DoE headliner

Using APRES, we find that the bands in Sr3Ru2O7 look more like in heavy fermion material than in a normal metal. We present a detailed investigation into the formation of this particular electronic structure.

MP Allan, A Tamai, E Rozbicki, MH Fischer, J Voss, PDC King, W Meevasana, S Thirupathaiah, E Rienks, J Fink, A Tennant, RS Perry, JF Mercure, MA Wang, J Lee, CJ Fennie, E-A Kim, MJ Lawler, KM Shen, AP Mackenzie, Z-X Shen, F Baumberger

New Journal of Physics 15, 063029 (2013)

We elucidate on the formation of the electronic nematic state in Co-CaFe2As2, finding that the Cobalt dopant atoms play a key role.

MP Allan, T-M Chuang, F Massee, Y Xie, N Ni, SL Bud’ko, GS Boebinger, Q Wang, DS Dessau, PC Canfield, MS Golden, JC Davis

Nature Physics 9, 220 (2013)

See also Tech Connect by Jennifer Rocha, Phys.org by Bill Steele

In contrast to earlier photoemission reports, we show that the gaps in iron based superconductors are not isotropic but modulated with angle.

MP Allan⋆ & AW Rost⋆, AP Mackenzie, Y Xie, JC Davis, K Kihou, CH Lee, A Iyo, H Eisaki, T-M Chuang

Science 336, 563 (2012)

See also Cornell Cornincle by Bill Steele, Eureka Alert

We discovered an electronic nematic in the iron based superconductor Co-CaFe2As2! This state is by now confirmed and quite well characterized by transport, photoemission, and more SI-STM experiments.

T-M Chuang* & MP Allan*, J Lee, Y Xie, N Ni, SL Bud’ko, GS Boebinger PC Canfield, JC Davis

Science 327, 181 (2010)

Featured in a ‘Perspective’ by E Fradkin & SA Kivelson

See also Article on NewScientist by Colin Barras

Hexagonal boron nitride shows fancy superstructures on the Mo(111) surface.

MP Allan, S Berner, M Corso, T Greber, J Osterwalder

Nanoscale Research Letters 2, 94 (2007)