---
_id: '14374'
abstract:
- lang: eng
text: "Superconductivity has many important applications ranging from levitating
trains over qubits to MRI scanners. The phenomenon is successfully modeled by
Bardeen-Cooper-Schrieffer (BCS) theory. From a mathematical perspective, BCS theory
has been studied extensively for systems without boundary. However, little is
known in the presence of boundaries. With the help of numerical methods physicists
observed that the critical temperature may increase in the presence of a boundary.
The goal of this thesis is to understand the influence of boundaries on the critical
temperature in BCS theory and to give a first rigorous justification of these
observations. On the way, we also study two-body Schrödinger operators on domains
with boundaries and prove additional results for superconductors without boundary.\r\n\r\nBCS
theory is based on a non-linear functional, where the minimizer indicates whether
the system is superconducting or in the normal, non-superconducting state. By
considering the Hessian of the BCS functional at the normal state, one can analyze
whether the normal state is possibly a minimum of the BCS functional and estimate
the critical temperature. The Hessian turns out to be a linear operator resembling
a Schrödinger operator for two interacting particles, but with more complicated
kinetic energy. As a first step, we study the two-body Schrödinger operator in
the presence of boundaries.\r\nFor Neumann boundary conditions, we prove that
the addition of a boundary can create new eigenvalues, which correspond to the
two particles forming a bound state close to the boundary.\r\n\r\nSecond, we need
to understand superconductivity in the translation invariant setting. While in
three dimensions this has been extensively studied, there is no mathematical literature
for the one and two dimensional cases. In dimensions one and two, we compute the
weak coupling asymptotics of the critical temperature and the energy gap in the
translation invariant setting. We also prove that their ratio is independent of
the microscopic details of the model in the weak coupling limit; this property
is referred to as universality.\r\n\r\nIn the third part, we study the critical
temperature of superconductors in the presence of boundaries. We start by considering
the one-dimensional case of a half-line with contact interaction. Then, we generalize
the results to generic interactions and half-spaces in one, two and three dimensions.
Finally, we compare the critical temperature of a quarter space in two dimensions
to the critical temperatures of a half-space and of the full space."
alternative_title:
- ISTA Thesis
article_processing_charge: No
author:
- first_name: Barbara
full_name: Roos, Barbara
id: 5DA90512-D80F-11E9-8994-2E2EE6697425
last_name: Roos
orcid: 0000-0002-9071-5880
citation:
ama: Roos B. Boundary superconductivity in BCS theory. 2023. doi:10.15479/at:ista:14374
apa: Roos, B. (2023). Boundary superconductivity in BCS theory. Institute
of Science and Technology Austria. https://doi.org/10.15479/at:ista:14374
chicago: Roos, Barbara. “Boundary Superconductivity in BCS Theory.” Institute of
Science and Technology Austria, 2023. https://doi.org/10.15479/at:ista:14374.
ieee: B. Roos, “Boundary superconductivity in BCS theory,” Institute of Science
and Technology Austria, 2023.
ista: Roos B. 2023. Boundary superconductivity in BCS theory. Institute of Science
and Technology Austria.
mla: Roos, Barbara. Boundary Superconductivity in BCS Theory. Institute of
Science and Technology Austria, 2023, doi:10.15479/at:ista:14374.
short: B. Roos, Boundary Superconductivity in BCS Theory, Institute of Science and
Technology Austria, 2023.
date_created: 2023-09-28T14:23:04Z
date_published: 2023-09-30T00:00:00Z
date_updated: 2023-10-27T10:37:30Z
day: '30'
ddc:
- '515'
- '539'
degree_awarded: PhD
department:
- _id: GradSch
- _id: RoSe
doi: 10.15479/at:ista:14374
ec_funded: 1
file:
- access_level: open_access
checksum: ef039ffc3de2cb8dee5b14110938e9b6
content_type: application/pdf
creator: broos
date_created: 2023-10-06T11:35:56Z
date_updated: 2023-10-06T11:35:56Z
file_id: '14398'
file_name: phd-thesis-draft_pdfa_acrobat.pdf
file_size: 2365702
relation: main_file
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checksum: 81dcac33daeefaf0111db52f41bb1fd0
content_type: application/x-zip-compressed
creator: broos
date_created: 2023-10-06T11:38:01Z
date_updated: 2023-10-06T11:38:01Z
file_id: '14399'
file_name: Version5.zip
file_size: 4691734
relation: source_file
file_date_updated: 2023-10-06T11:38:01Z
has_accepted_license: '1'
language:
- iso: eng
month: '09'
oa: 1
oa_version: Published Version
page: '206'
project:
- _id: 25C6DC12-B435-11E9-9278-68D0E5697425
call_identifier: H2020
grant_number: '694227'
name: Analysis of quantum many-body systems
- _id: bda63fe5-d553-11ed-ba76-a16e3d2f256b
grant_number: I06427
name: Mathematical Challenges in BCS Theory of Superconductivity
publication_identifier:
issn:
- 2663 - 337X
publication_status: published
publisher: Institute of Science and Technology Austria
related_material:
record:
- id: '13207'
relation: part_of_dissertation
status: public
- id: '10850'
relation: part_of_dissertation
status: public
status: public
supervisor:
- first_name: Robert
full_name: Seiringer, Robert
id: 4AFD0470-F248-11E8-B48F-1D18A9856A87
last_name: Seiringer
orcid: 0000-0002-6781-0521
title: Boundary superconductivity in BCS theory
tmp:
image: /images/cc_by_nc_sa.png
legal_code_url: https://creativecommons.org/licenses/by-nc-sa/4.0/legalcode
name: Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International (CC
BY-NC-SA 4.0)
short: CC BY-NC-SA (4.0)
type: dissertation
user_id: 8b945eb4-e2f2-11eb-945a-df72226e66a9
year: '2023'
...
---
_id: '14542'
abstract:
- lang: eng
text: "It is a remarkable property of BCS theory that the ratio of the energy gap
at zero temperature Ξ\r\n and the critical temperature Tc is (approximately) given
by a universal constant, independent of the microscopic details of the fermionic
interaction. This universality has rigorously been proven quite recently in three
spatial dimensions and three different limiting regimes: weak coupling, low density
and high density. The goal of this short note is to extend the universal behavior
to lower dimensions d=1,2 and give an exemplary proof in the weak coupling limit."
acknowledgement: We thank Robert Seiringer for comments on the paper. J. H. gratefully
acknowledges partial financial support by the ERC Advanced Grant “RMTBeyond”No.
101020331.This research was funded in part by the Austrian Science Fund (FWF) grantnumber
I6427.
article_number: '2360005 '
article_processing_charge: Yes (in subscription journal)
article_type: original
arxiv: 1
author:
- first_name: Sven Joscha
full_name: Henheik, Sven Joscha
id: 31d731d7-d235-11ea-ad11-b50331c8d7fb
last_name: Henheik
orcid: 0000-0003-1106-327X
- first_name: Asbjørn Bækgaard
full_name: Lauritsen, Asbjørn Bækgaard
id: e1a2682f-dc8d-11ea-abe3-81da9ac728f1
last_name: Lauritsen
orcid: 0000-0003-4476-2288
- first_name: Barbara
full_name: Roos, Barbara
id: 5DA90512-D80F-11E9-8994-2E2EE6697425
last_name: Roos
orcid: 0000-0002-9071-5880
citation:
ama: Henheik SJ, Lauritsen AB, Roos B. Universality in low-dimensional BCS theory.
Reviews in Mathematical Physics. 2023. doi:10.1142/s0129055x2360005x
apa: Henheik, S. J., Lauritsen, A. B., & Roos, B. (2023). Universality in low-dimensional
BCS theory. Reviews in Mathematical Physics. World Scientific Publishing.
https://doi.org/10.1142/s0129055x2360005x
chicago: Henheik, Sven Joscha, Asbjørn Bækgaard Lauritsen, and Barbara Roos. “Universality
in Low-Dimensional BCS Theory.” Reviews in Mathematical Physics. World
Scientific Publishing, 2023. https://doi.org/10.1142/s0129055x2360005x.
ieee: S. J. Henheik, A. B. Lauritsen, and B. Roos, “Universality in low-dimensional
BCS theory,” Reviews in Mathematical Physics. World Scientific Publishing,
2023.
ista: Henheik SJ, Lauritsen AB, Roos B. 2023. Universality in low-dimensional BCS
theory. Reviews in Mathematical Physics., 2360005.
mla: Henheik, Sven Joscha, et al. “Universality in Low-Dimensional BCS Theory.”
Reviews in Mathematical Physics, 2360005, World Scientific Publishing,
2023, doi:10.1142/s0129055x2360005x.
short: S.J. Henheik, A.B. Lauritsen, B. Roos, Reviews in Mathematical Physics (2023).
date_created: 2023-11-15T23:48:14Z
date_published: 2023-10-31T00:00:00Z
date_updated: 2023-11-20T10:04:38Z
day: '31'
department:
- _id: GradSch
- _id: LaEr
- _id: RoSe
doi: 10.1142/s0129055x2360005x
ec_funded: 1
external_id:
arxiv:
- '2301.05621'
has_accepted_license: '1'
language:
- iso: eng
main_file_link:
- open_access: '1'
url: https://doi.org/10.1142/S0129055X2360005X
month: '10'
oa: 1
oa_version: Published Version
project:
- _id: 62796744-2b32-11ec-9570-940b20777f1d
call_identifier: H2020
grant_number: '101020331'
name: Random matrices beyond Wigner-Dyson-Mehta
- _id: bda63fe5-d553-11ed-ba76-a16e3d2f256b
grant_number: I06427
name: Mathematical Challenges in BCS Theory of Superconductivity
publication: Reviews in Mathematical Physics
publication_identifier:
eissn:
- 1793-6659
issn:
- 0129-055X
publication_status: epub_ahead
publisher: World Scientific Publishing
quality_controlled: '1'
scopus_import: '1'
status: public
title: Universality in low-dimensional BCS theory
tmp:
image: /images/cc_by.png
legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
short: CC BY (4.0)
type: journal_article
user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87
year: '2023'
...
---
_id: '13207'
abstract:
- lang: eng
text: We consider the linear BCS equation, determining the BCS critical temperature,
in the presence of a boundary, where Dirichlet boundary conditions are imposed.
In the one-dimensional case with point interactions, we prove that the critical
temperature is strictly larger than the bulk value, at least at weak coupling.
In particular, the Cooper-pair wave function localizes near the boundary, an effect
that cannot be modeled by effective Neumann boundary conditions on the order parameter
as often imposed in Ginzburg–Landau theory. We also show that the relative shift
in critical temperature vanishes if the coupling constant either goes to zero
or to infinity.
acknowledgement: We thank Egor Babaev for encouraging us to study this problem, and
Rupert Frank for many fruitful discussions. scussions. Funding. Funding from the
European Union’s Horizon 2020 research and innovation programme under the ERC grant
agreement No. 694227 (Barbara Roos and Robert Seiringer) is gratefully acknowledged.
article_processing_charge: No
article_type: original
arxiv: 1
author:
- first_name: Christian
full_name: Hainzl, Christian
last_name: Hainzl
- first_name: Barbara
full_name: Roos, Barbara
id: 5DA90512-D80F-11E9-8994-2E2EE6697425
last_name: Roos
orcid: 0000-0002-9071-5880
- first_name: Robert
full_name: Seiringer, Robert
id: 4AFD0470-F248-11E8-B48F-1D18A9856A87
last_name: Seiringer
orcid: 0000-0002-6781-0521
citation:
ama: Hainzl C, Roos B, Seiringer R. Boundary superconductivity in the BCS model.
Journal of Spectral Theory. 2023;12(4):1507–1540. doi:10.4171/JST/439
apa: Hainzl, C., Roos, B., & Seiringer, R. (2023). Boundary superconductivity
in the BCS model. Journal of Spectral Theory. EMS Press. https://doi.org/10.4171/JST/439
chicago: Hainzl, Christian, Barbara Roos, and Robert Seiringer. “Boundary Superconductivity
in the BCS Model.” Journal of Spectral Theory. EMS Press, 2023. https://doi.org/10.4171/JST/439.
ieee: C. Hainzl, B. Roos, and R. Seiringer, “Boundary superconductivity in the BCS
model,” Journal of Spectral Theory, vol. 12, no. 4. EMS Press, pp. 1507–1540,
2023.
ista: Hainzl C, Roos B, Seiringer R. 2023. Boundary superconductivity in the BCS
model. Journal of Spectral Theory. 12(4), 1507–1540.
mla: Hainzl, Christian, et al. “Boundary Superconductivity in the BCS Model.” Journal
of Spectral Theory, vol. 12, no. 4, EMS Press, 2023, pp. 1507–1540, doi:10.4171/JST/439.
short: C. Hainzl, B. Roos, R. Seiringer, Journal of Spectral Theory 12 (2023) 1507–1540.
date_created: 2023-07-10T16:35:45Z
date_published: 2023-05-18T00:00:00Z
date_updated: 2023-10-27T10:37:29Z
day: '18'
ddc:
- '530'
department:
- _id: GradSch
- _id: RoSe
doi: 10.4171/JST/439
ec_funded: 1
external_id:
arxiv:
- '2201.08090'
isi:
- '000997933500008'
file:
- access_level: open_access
checksum: 5501da33be010b5c81440438287584d5
content_type: application/pdf
creator: alisjak
date_created: 2023-07-11T08:19:15Z
date_updated: 2023-07-11T08:19:15Z
file_id: '13208'
file_name: 2023_EMS_Hainzl.pdf
file_size: 304619
relation: main_file
success: 1
file_date_updated: 2023-07-11T08:19:15Z
has_accepted_license: '1'
intvolume: ' 12'
isi: 1
issue: '4'
language:
- iso: eng
month: '05'
oa: 1
oa_version: Published Version
page: 1507–1540
project:
- _id: 25C6DC12-B435-11E9-9278-68D0E5697425
call_identifier: H2020
grant_number: '694227'
name: Analysis of quantum many-body systems
publication: Journal of Spectral Theory
publication_identifier:
eissn:
- 1664-0403
issn:
- 1664-039X
publication_status: published
publisher: EMS Press
quality_controlled: '1'
related_material:
record:
- id: '14374'
relation: dissertation_contains
status: public
status: public
title: Boundary superconductivity in the BCS model
tmp:
image: /images/cc_by.png
legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
short: CC BY (4.0)
type: journal_article
user_id: 4359f0d1-fa6c-11eb-b949-802e58b17ae8
volume: 12
year: '2023'
...
---
_id: '10850'
abstract:
- lang: eng
text: "We study two interacting quantum particles forming a bound state in d-dimensional
free\r\nspace, and constrain the particles in k directions to (0, ∞)k ×Rd−k, with
Neumann boundary\r\nconditions. First, we prove that the ground state energy strictly
decreases upon going from k\r\nto k+1. This shows that the particles stick to
the corner where all boundary planes intersect.\r\nSecond, we show that for all
k the resulting Hamiltonian, after removing the free part of the\r\nkinetic energy,
has only finitely many eigenvalues below the essential spectrum. This paper\r\ngeneralizes
the work of Egger, Kerner and Pankrashkin (J. Spectr. Theory 10(4):1413–1444,\r\n2020)
to dimensions d > 1."
acknowledgement: We thank Rupert Frank for contributing Appendix B. Funding from the
European Union's Horizon 2020 research and innovation programme under the ERC grant
agreement No. 694227 is gratefully acknowledged.
article_number: '109455'
article_processing_charge: Yes (via OA deal)
article_type: original
arxiv: 1
author:
- first_name: Barbara
full_name: Roos, Barbara
id: 5DA90512-D80F-11E9-8994-2E2EE6697425
last_name: Roos
orcid: 0000-0002-9071-5880
- first_name: Robert
full_name: Seiringer, Robert
id: 4AFD0470-F248-11E8-B48F-1D18A9856A87
last_name: Seiringer
orcid: 0000-0002-6781-0521
citation:
ama: Roos B, Seiringer R. Two-particle bound states at interfaces and corners. Journal
of Functional Analysis. 2022;282(12). doi:10.1016/j.jfa.2022.109455
apa: Roos, B., & Seiringer, R. (2022). Two-particle bound states at interfaces
and corners. Journal of Functional Analysis. Elsevier. https://doi.org/10.1016/j.jfa.2022.109455
chicago: Roos, Barbara, and Robert Seiringer. “Two-Particle Bound States at Interfaces
and Corners.” Journal of Functional Analysis. Elsevier, 2022. https://doi.org/10.1016/j.jfa.2022.109455.
ieee: B. Roos and R. Seiringer, “Two-particle bound states at interfaces and corners,”
Journal of Functional Analysis, vol. 282, no. 12. Elsevier, 2022.
ista: Roos B, Seiringer R. 2022. Two-particle bound states at interfaces and corners.
Journal of Functional Analysis. 282(12), 109455.
mla: Roos, Barbara, and Robert Seiringer. “Two-Particle Bound States at Interfaces
and Corners.” Journal of Functional Analysis, vol. 282, no. 12, 109455,
Elsevier, 2022, doi:10.1016/j.jfa.2022.109455.
short: B. Roos, R. Seiringer, Journal of Functional Analysis 282 (2022).
date_created: 2022-03-16T08:41:53Z
date_published: 2022-06-15T00:00:00Z
date_updated: 2023-10-27T10:37:29Z
day: '15'
ddc:
- '510'
department:
- _id: GradSch
- _id: RoSe
doi: 10.1016/j.jfa.2022.109455
ec_funded: 1
external_id:
arxiv:
- '2105.04874'
isi:
- '000795160200009'
file:
- access_level: open_access
checksum: 63efcefaa1f2717244ef5407bd564426
content_type: application/pdf
creator: dernst
date_created: 2022-08-02T10:37:55Z
date_updated: 2022-08-02T10:37:55Z
file_id: '11720'
file_name: 2022_JourFunctionalAnalysis_Roos.pdf
file_size: 631391
relation: main_file
success: 1
file_date_updated: 2022-08-02T10:37:55Z
has_accepted_license: '1'
intvolume: ' 282'
isi: 1
issue: '12'
keyword:
- Analysis
language:
- iso: eng
month: '06'
oa: 1
oa_version: Published Version
project:
- _id: 25C6DC12-B435-11E9-9278-68D0E5697425
call_identifier: H2020
grant_number: '694227'
name: Analysis of quantum many-body systems
publication: Journal of Functional Analysis
publication_identifier:
issn:
- 0022-1236
publication_status: published
publisher: Elsevier
quality_controlled: '1'
related_material:
record:
- id: '14374'
relation: dissertation_contains
status: public
scopus_import: '1'
status: public
title: Two-particle bound states at interfaces and corners
tmp:
image: /images/cc_by.png
legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
short: CC BY (4.0)
type: journal_article
user_id: 4359f0d1-fa6c-11eb-b949-802e58b17ae8
volume: 282
year: '2022'
...
---
_id: '12276'
abstract:
- lang: eng
text: Ongoing development of quantum simulators allows for a progressively finer
degree of control of quantum many-body systems. This motivates the development
of efficient approaches to facilitate the control of such systems and enable the
preparation of nontrivial quantum states. Here we formulate an approach to control
quantum systems based on matrix product states (MPSs). We compare counterdiabatic
and leakage minimization approaches to the so-called local steering problem that
consists in finding the best value of the control parameters for generating a
unitary evolution of the specific MPS in a given direction. In order to benchmark
the different approaches, we apply them to the generalization of the PXP model
known to exhibit coherent quantum dynamics due to quantum many-body scars. We
find that the leakage-based approach generally outperforms the counterdiabatic
framework and use it to construct a Floquet model with quantum scars. We perform
the first steps towards global trajectory optimization and demonstrate entanglement
steering capabilities in the generalized PXP model. Finally, we apply our leakage
minimization approach to construct quantum scars in the periodically driven nonintegrable
Ising model.
acknowledgement: We thank A. A. Michailidis for insightful discussions. M.L. and M.S.
acknowledge support from the European Research Council (ERC) under the European
Union’s Horizon 2020 research and innovation programme (Grant Agreement No. 850899).
D.A. is supported by the European Research Council (ERC) under the European Union’s
Horizon 2020 research and innovation programme (Grant Agreement No. 864597) and
by the Swiss National Science Foundation. The infinite TEBD simulations were performed
using the ITensor library [67].
article_number: '030343'
article_processing_charge: No
article_type: original
arxiv: 1
author:
- first_name: Marko
full_name: Ljubotina, Marko
id: F75EE9BE-5C90-11EA-905D-16643DDC885E
last_name: Ljubotina
- first_name: Barbara
full_name: Roos, Barbara
id: 5DA90512-D80F-11E9-8994-2E2EE6697425
last_name: Roos
orcid: 0000-0002-9071-5880
- first_name: Dmitry A.
full_name: Abanin, Dmitry A.
last_name: Abanin
- first_name: Maksym
full_name: Serbyn, Maksym
id: 47809E7E-F248-11E8-B48F-1D18A9856A87
last_name: Serbyn
orcid: 0000-0002-2399-5827
citation:
ama: Ljubotina M, Roos B, Abanin DA, Serbyn M. Optimal steering of matrix product
states and quantum many-body scars. PRX Quantum. 2022;3(3). doi:10.1103/prxquantum.3.030343
apa: Ljubotina, M., Roos, B., Abanin, D. A., & Serbyn, M. (2022). Optimal steering
of matrix product states and quantum many-body scars. PRX Quantum. American
Physical Society. https://doi.org/10.1103/prxquantum.3.030343
chicago: Ljubotina, Marko, Barbara Roos, Dmitry A. Abanin, and Maksym Serbyn. “Optimal
Steering of Matrix Product States and Quantum Many-Body Scars.” PRX Quantum.
American Physical Society, 2022. https://doi.org/10.1103/prxquantum.3.030343.
ieee: M. Ljubotina, B. Roos, D. A. Abanin, and M. Serbyn, “Optimal steering of matrix
product states and quantum many-body scars,” PRX Quantum, vol. 3, no. 3.
American Physical Society, 2022.
ista: Ljubotina M, Roos B, Abanin DA, Serbyn M. 2022. Optimal steering of matrix
product states and quantum many-body scars. PRX Quantum. 3(3), 030343.
mla: Ljubotina, Marko, et al. “Optimal Steering of Matrix Product States and Quantum
Many-Body Scars.” PRX Quantum, vol. 3, no. 3, 030343, American Physical
Society, 2022, doi:10.1103/prxquantum.3.030343.
short: M. Ljubotina, B. Roos, D.A. Abanin, M. Serbyn, PRX Quantum 3 (2022).
date_created: 2023-01-16T10:01:56Z
date_published: 2022-09-23T00:00:00Z
date_updated: 2023-01-30T11:05:23Z
day: '23'
ddc:
- '530'
department:
- _id: MaSe
- _id: RoSe
doi: 10.1103/prxquantum.3.030343
ec_funded: 1
external_id:
arxiv:
- '2204.02899'
file:
- access_level: open_access
checksum: ef8f0a1b5a019b3958009162de0fa4c3
content_type: application/pdf
creator: dernst
date_created: 2023-01-30T11:02:50Z
date_updated: 2023-01-30T11:02:50Z
file_id: '12457'
file_name: 2022_PRXQuantum_Ljubotina.pdf
file_size: 7661905
relation: main_file
success: 1
file_date_updated: 2023-01-30T11:02:50Z
has_accepted_license: '1'
intvolume: ' 3'
issue: '3'
keyword:
- General Medicine
language:
- iso: eng
month: '09'
oa: 1
oa_version: Published Version
project:
- _id: 23841C26-32DE-11EA-91FC-C7463DDC885E
call_identifier: H2020
grant_number: '850899'
name: 'Non-Ergodic Quantum Matter: Universality, Dynamics and Control'
publication: PRX Quantum
publication_identifier:
eissn:
- 2691-3399
publication_status: published
publisher: American Physical Society
quality_controlled: '1'
scopus_import: '1'
status: public
title: Optimal steering of matrix product states and quantum many-body scars
tmp:
image: /images/cc_by.png
legal_code_url: https://creativecommons.org/licenses/by/4.0/legalcode
name: Creative Commons Attribution 4.0 International Public License (CC-BY 4.0)
short: CC BY (4.0)
type: journal_article
user_id: 2DF688A6-F248-11E8-B48F-1D18A9856A87
volume: 3
year: '2022'
...